Doom Slayer

"Rip... and... tear!"

- The Slayer, after defeating a fellow Sentinel initiate in the arena

The Doom Slayer is the protagonist and playable character of Doom, Doom II: Hell on Earth, Doom 3, Final Doom, Doom 64, Doom (2016), Quake 3 Arena, Quake Champions and Doom Eternal. He is also known by the UAC as DM1-5, DOOM Marine or The Slayer, and by the Demons of Hell as the Doom Slayer, the Unchained Predator, the Beast or the Hell Walker. Depending on the version of the character, his real name or aliases include William Joseph Blazkowicz and Flynn Taggart. He is known in the flashback subtitles as Doomguy.

He is intended to be the latest iteration and continuation of the classic Doom Marine who is the protagonist for most of the series. According to Tom Hall and John Romero (who worked on the original Doom), the original iteration of the Doom Marine was the grandson of Commander Keen, and the great-great-grandson of B.J Blazkowicz. It is unknown if the modern iteration is as well, although it seems unlikely. He also has no name and is a representation of the player according to the developers.

He is a human with an AB positive blood type and is revealed to be none other than the original nameless marine from classic Doom games.

Classic Doom (Doom, Doom II, and Doom 64)
The Doom Slayer was originally a human from Earth (from an unknown time and place, or universe in the multiverse). He once fought through Phobos, Deimos and Hell. He returned to find his pet Daisy dead. He decided to take revenge on the demons further. He fought the monsters again, this through Earth, returning to Hell once more.

Following this, and possibly other outbreaks he was part of, he was decommissioned. Some years later he was called upon again to fight through a planetary space station (some say a return to Phobos) ) Again he fought the Hellish forces, back to hell. This time defeating the Mother of All Demons. He decided in order to save Earth he needed to remain in hell and fight the creatures for eternity (Doom 64).

The Mother's sister, Resurrector was not happy, in revenge she teleported him back to Earth, and tried to kill him. But he fought his way back to Hell again, he chased the sister down, and defeated her. Again he chose to remain in hell (The Lost Episode).

Before Doom (2016)
At some point, he became stranded in Sentinel Prime on Argent D'Nur after remaining in Hell. There he is captured by the Night Sentinels (or Argenta) and ended up in a different dimension (arguably the one containing Doom 3, 2016, and Eternal).

After being put through a trial by combat, where he proved extraordinarily skilled. He was later sent to the frontlines of the conquests of Argent D'Nur, where he proved once again his skill in battle. This garnered the attention of the clergy and ruling powers of Argent D'Nur, and despite being an outlander he was taken in and trained by the Night Sentinel order of knights. Despite all this, the Doom Slayer remains firmly obsessed with the demons and their imminent arrival to Argent D'Nur, and much so the demons do eventually arrive. This is when the Doom Slayer gained his (in)famous title, as he proved once and for all his skill at slaying the leagues of doom.

During this time he also helped the Bethians and Night Sentinels that had colonized Mars, creating the city of Hebeth there. He helped the ancient Martians fight back a demon invasion there. He was honored in Site 3 (with a statue dipicting his Praetor Suit), and the Chamber of the Hero. Still the martian civilisation fell not before creating the Soul Cube in which it was used by the Marine Corporal in Doom 3 and after it sealed the Gate of Hell, it was acquired by Doom Slayer in Hell. Some survivors possibly making it to Earth, others returned to Argent D'Nur.

Though the maykr race who had long been allied to the Night Sentinels eventually came to betray them in order to work with Hell to harvest Argent energy, the Doom Slayer remained loyal to the Sentinels. At the behest of the Order of the Deag, the Doom Slayer accompanied the Night Sentinels to Hell in the hopes of securing a final victory against the demons. However, they realised too late that the priests had betrayed them to the Khan Maykr. The Slayer and the Night Sentinels were left stranded in Hell and endlessly fought the infinite demon hordes. One by one, the Night Sentinels were killed, save for the Doom Slayer and Valen, the latter of whom allowed the demons access to the Elemental Wraiths in exchange for his son's ressurection. When Argent D'Nur fell, Valen, now known as the Betrayer, chose to stay in Hell for the remainder of his days in self-imposed exile. The Doom Slayer, on the other hand, continued his endless killing spree.

Over time, the demons themselves grew to fear him. A Titan was chosen as Hell's champion and sent to kill the Slayer, only to be killed by him. Having failed to kill the Slayer at every attempt, the Demons instead lured him into a blood temple before collapsing the entire structure on top of him. Trapped beneath the ruin, the Slayer was entombed within a sarcophagus, frozen in stasis within the Kadingr Sanctum.

During the UAC's Argent energy harvesting operations on Mars, Dr. Samuel Hayden led an expedition into Hell to acquire demon specimens and artifacts for further research on Hell. One of these artifacts was the Doom Slayer's sarcophagus, which Samuel noticed was guarded much more ferociously than other points of interest within Hell. Upon identifying the Slayer and his armour within, and developing a suspicion of his employee and former protege Olivia Pierce,Samuel had the sarcophagus hidden in a concealed location within the UAC facility. Upon suspecting Olivia's pact with Hell and her plans for the Mars facility, Samuel intended to release the Doom Slayer in the event of the UAC losing control of its demonic experiments.

Doom (2016)
The Slayer is awakened after an unknown amount of time by Samuel Hayden during a demonic invasion of Mars triggered by Olivia Pierce. Upon breaking out of the facility he proceeds to Resource Operations to repair a dish in order to get a complete picture of the situation. Hayden stops the Slayer from accessing the information in question and guides him to a VEGA terminal in order to give the Slayer a argent cell to improve his suit. The Slayer proceeds through the Foundry stopping a meltdown by activating the terminals and then onto the Argent tower itself. Despite instructions from Hayden the Slayer smashes the filters channeling the Argent energy to stop Pierce from opening a portal. Despite this upon reaching the top of the tower and confronting Pierce she uses a Argent Accumulator to break open the rift into hell warping the Slayer to the Kadingir Sanctum.

He fights his way through the Sanctum to the location where his Sarcophagus was located in order to use the portal equipment left from a manned expedition into hell. Upon returning to Mars he finds the UAC facility overrun with demons as the demonic portal allows them easy access to the red planet. He finally meets Hayden face to face and Hayden implants a program into his suit allowing him to teleport the Slayer back to Mars. He fights his way to the Advanced Research Complex and retrieves the BFG 9000 before proceeding into the heart of the cult activity on Mars. He proceeds to the Lazarus Labs and fights the Cyberdemon he then uses the accumulator that powered the boss demon to teleport back into hell. He then fights his way through the Titan realm and the Necropolis on his way to obtain the Demonic Crucible. After defeating it's guardians he retrieves the Crucible and is greeted by ghosts of the Sentinel Knights. Before any exchange can happen he is teleported back to Mars specifically to VEGA's primary facility. In order to reach The Well and cut off the power source keeping the portal on Mars open he has to overload VEGA's systems to rip open a portal to the Well. Before overloading VEGA's core however the Slayer pauses and makes a copy of VEGA onto a backup device he takes with him for reasons unknown.

Finally at the well the Slayer fights his way to each of the Wraith bodies and uses the Crucible to absorb their energy to cut off the flow to the portal. Once the final wraith has been disabled the Slayer is greeted by several Sentinels who stand guard around a pit leading to the final battle. Here he meets Pierce bloodied and in shock that she was betrayed by her demonic masters. These same masters then hit her with a crimson lightning bolt turning her into the Spider Mastermind though is ultimately defeated by the Slayer. After this Hayden pulls the Slayer back to Mars and keeps him restrained by the teleporter. He takes the Crucible from the Slayer saying he cannot kill him but he won't let him stand in his way. He then activates the Crucible blade before teleporting the Slayer to a unstated location (though it can be theorized to be the Fortress of Doom).

Doom Eternal
''As a new demonic threat erupts on Earth, the Slayer, his iconic Praetor Suit modified and upgraded for increased mobility and destructive capability. For the Slayer, it is a battle that has continued for an eternity, a fight that can only be won by confronting his past if he hopes to stop history from repeating itself.''

''VEGA has created an inter-dimensional man-machine gateway that allows the Slayer to engage in skirmishes across the multiverse directly. As the Slayer enters the gateway, his surroundings take the form of an arena, in tandem with the arrival of adversaries ready for battle Seemingly extracted from the data of his experiences, the opponents the Slayer faces are familiar but now transformed by some unseen force.''

''With further analysis Vega observed ephemeral distortions within the fabric of reality; scrambled reflections of the physical world. As the slayer interacts with this anomaly, a peculiar ripple in the anomaly's composition emerges, seemingly reacting to the Slayer's presence reflexively. The anomaly reshapes itself, calibrating itself to the Slayer, responding to his memory, ancestral, and memetic data, before ultimately projecting itself onto the Slayer himself.''

Doom Slayer's alliance with the Night Sentinels lasted as long as up to the events of Doom Eternal, when he would come to defy even their orders in order to save his fellow Earthborn humans.

UAC REPORT FILE H8UM66S
In the first age, in the first battle, when the shadows first lengthened, one stood. Burned by the embers of Armageddon, his soul blistered by the fires of Hell and tainted beyond ascension, he chose the path of perpetual torment. In his ravenous hatred, he found no peace, and with boiling blood he scoured the Umbral Plains seeking vengeance against the dark lords who had wronged him. He wore the crown of the Night Sentinels, and those that tasted the bite of his sword named him... the Doom Slayer.

UAC REPORT FILE 9REIZDUR
Tempered by the fires of Hell, his iron will remain steadfast through the passage that preys upon the weak. For he alone was the Hell Walker, the Unchained Predator, who sought retribution in all quarters, dark and light, fire and ice, in the beginning, and the end, and he hunted the slaves of Doom with barbarous cruelty; for he passed through the divide as none but the demon had before.

UAC REPORT FILE HR93TE1F
And in his conquest against the blackened souls of the doomed, his prowess was shown. In his crusade, the seraphim (angel) bestowed upon him terrible power and speed, and with his might, he crushed the obsidian pillars of the Blood Temples. He set forth without pity upon the beasts of the nine circles. Unbreakable, incorruptible, unyielding, the Doom Slayer sought to end the dominion of the dark realm.

UAC REPORT FILE I3S5A9XB
The age of his reckoning was uncounted. The scribes carved his name deep in the tablets of Hell across eons, and each battle etched terror in the hearts of the demons. They knew he would come, as he always had, as he always will, to feast on the blood of the wicked. For he alone could draw strength from his fallen foes, and ever his power grew, swift and unrelenting.

UAC REPORT FILE ZPHVM41A
None could stand before the horde but the Doom Slayer. Despair spread before him like a plague, striking fear into the shadow-dwellers, driving them to deeper and darker pits. But from the depths of the abyss rose The Great One, a champion mightier than all who had come before. The Titan, of immeasurable power and ferocity. He strode upon the plain and faced the Doom Slayer, and a mighty battle was fought on the desolate plains. The Titan fought with the fury of the countless that had fallen at the Doom Slayer's hand, but there fell the Titan, and in his defeat, the shadow horde was routed.

UAC REPORT FILE WMHVVFJ
And in his terrible rancor between worlds and through time, the Hell Walker found the wretch who shall not be named, but in his heresy was loyal to his evil cause. The wretch adorned the Doom Slayer in a mighty armor, wrought in the forges of Hell, impenetrable and unyielding. With sword and shield of adamantine strength, the Doom Slayer set to banishing all that was left unbroken by his savagery to the void.

UAC REPORT FILE JSLR7ESL
Yet as the mighty Titan fell and dread engulfed the armies of Doom, the demon priests of the Blood Temples laid a trap to capture this scourge of Hell. Insatiable, even by the vanquishing of the Great One, the Hell Walker sought prey in the tombs of the Blood Keep. And blinded by his fervor, the lure drew him in. The priests brought down the temple upon the Doom Slayer, and in his defeat entombed him in the cursed sarcophagus. The mark of the Doom Slayer was burned upon his crypt, a warning to all of Hell that the terror within must never be freed. There he lies still, and evermore, in silent suffering.

Personality and traits
Unlike some of his earlier appearances in the series, he shows a little more emotion, expressed more through actions rather than words. During his crusade and his interactions with Samuel Hayden (who tries to use and ask the Marine for help) when the latter tries to justifies the UAC's actions in hell as being in mankind's best interests despite the evident risks and aftermath consequences, the Marine responds by angrily dismantling communication equipment at best, and flat-out destroying key UAC equipment at worst despite Hayden's insistence of not doing so.

This makes it clear that the Doom Slayer's motivations and priorities start and end with stopping and killing demons and not for the UAC and their economic interests, and very little for anything else. He does, however, show to be sympathetic to a degree as seen when he made a back-up copy of VEGA before destroying, although this could be attributed to the fact the AI opted to sacrifice itself to aid the Doom Slayer in his quest. As such it can be deduced the Marine can show concern for those that either aid him on his demon-slaying mission or otherwise show the necessary resolve to act for the real greater good. Despite protecting mankind from demons for years, Slayer seems to have very little if any interest of humanity as such, possibly view them as immature and foolish as they bring demons to their world on their own due to their greed for hellish energy. yet he never injures or killed any of the people he meets,  at most intimidated them or push them away when they were in his way.

The Doom Slayer also appears to be quite intelligent as his original Praetor Suit could be found disassembled in his personal quarters with numerous parts of it repurposed for his new Praetor Suit.

Unlike the first two games, the Doom Slayer never makes any vocal utterances in Doom (2016), even when taking damage or dying. This seems to change to slight grunts in Doom Eternal. However, in Doom Eternal, and for the very first time in the series of games, we do get to hear the Doom Slayer's speaking voice during flashbacks upon entering Sentinel Prime.

Titles and Nicknames

 * Doom/DOOM
 * Doom Marine/DOOM Marine
 * Doom Slayer
 * Hell Walker/Hellwalker
 * Unchained Predator
 * Scourge of Hell
 * The Destroyer
 * The Slayer
 * The Beast
 * DM1-5 (possibly a reference to Doom 1 to 5)
 * Doomguy
 * Flynn Taggart (Login ID)/Taggart93
 * The Outlander
 * William Blazkowicz/Stan Blazkowicz (possible real name)
 * The Destroyer
 * Sarge
 * Harbinger
 * Space Marine
 * Night Sentinel

Doom Eternal Titles

 * Eternal Slayer
 * Empyrean Warrior
 * Extra Lifer
 * Gate Breaker
 * Gunslinger
 * He's on Fire
 * Immortal
 * Lore Master
 * Titan Slayer
 * Unmodded
 * Class of '94
 * Hell's Mightiest Warrior
 * Hot Stuff
 * Lord of Fire
 * MERCILESS EXTERMINATOR
 * Peace Man
 * Shareware Warrior
 * Slayer's Club
 * Soul Taker
 * Super Sparkle Slayer
 * Vet

Faces of the Slayer
The face of the Doom Slayer has evolved and changed over the years, with the character originally having reddish/brown hair, but later having dark brown hair.

The Doom Marine's face is obscured (in Doom (2016), Doom Eternal, and other games.

In Doom 2016, Doom Slayer's face was discovered through model and texture "ripping", and shows a remarkable sense of similarity to the Classic Doomguy's face. In classic maps he uses a texture based on his face from Doom 1. His facial model and jawline and general structure of his face resembles B.J. Blazkowicz from Wolfenstein: The New Order to some extent. This may be a reference to how the original Doom and Wolfenstein player models were very alike, also having been told to be related somehow.

Quake Champions gave him a number of different faces, some based on his classic appearance in original doom, Doom Marine's's appearance in Doom 3, and a unique model for his Doom Slayer appearance as well. The classic "Doom" model (from Quake Arena) does not show his face.

In Doom Eternal he is given yet another face (somewhat similar to Doom 3's appearance/hair color, mixed with facial model of B.J. Blazkowicz from Wolfenstein (2009).

The Art of Doom Eternal gives several facial designs that were ultimately rejected.

A life-size statue of Doom Slayer was made, a picture of which, where John Romero is standing next to it, shows the Doom Slayer's face.

In Doom (2016) and Doom Eternal, his face can also be seen in reflection of his helmet under certain conditions.

Quake Champions Character Background
The UAC's most remarkable discovery was in Hell's Kadingir Sanctum. Surrounded by nearly impassable terrain, the team discovered a sealed tomb – its entrance and walls covered in protective runes and imprisonment incantations.

The tomb revealed many artifacts, including the Praetor suit. Most notable, however, was an enormous sarcophagus bound to the center bedrock of the tomb with thick iron bands – seemingly anchored to prevent anything from getting in or out.

It was believed this sarcophagus must hold a rare or powerful demon, but when later opened, it revealed the body of a man. Unrelenting; unforgiving; driven by a rage that cannot be contained. The Doom Slayer has been to Hell and brought it to its knees. He has no records, and he seems to vanish as quickly as he appears. The few witnesses account available detail a ruthless killer. Long ago across worlds and time, in another universe, Doom Slayer (B.J. Blazkowicz (Doom)) had become a great hero when he saved earth from an invasion by demons from hell. He continued to carry the left hind foot of his pet rabbit Daisy, killed by the marauding demons when their invasion of Earth began. He carried it as a reminder of innocence lost, not for luck--after all, it wasn't lucky for Daisy. The armor he wore became iconic, and it changed the world.

At some point the wide-eyed Doom Marine, found himself again newly transferred to Mars, the soldier got more than he asked for when Dr. Betruger betrayed the UAC.

During his battles to protect Earth, he found himself trapped in hell fighting an eternal battle with the demons. He would travel across time and worlds to save the multiverse. Sometimes finding himself pulled to battle other Champions from other worlds and alternate earth in the Arena Eternal (in this earlier period, he received new armor, that fit like a glove). He continued to be a great champion defending many worlds from the demons and killing them in Hell.

The Slayer's Testaments described him as an ancient and mystical time-traveling warrior called the "Doom Slayer" or "Hell Walker" who was either banished to Hell or chose to stay there. The Doom Marine proceeded to rampage his way across Hell for "eons" as an unstoppable force of death and destruction, becoming an icon of fear to all demons.

His one-man war was only ended after he was lured into a trap, allowing the forces of Hell to collapse one of their temples on top of him. Entombed inside a stone sarcophagus, he was sealed away in the Kadingir Sanctum, hopefully forever. Unfortunately for the demons, the Doom Marine's sarcophagus was eventually retrieved by the UAC (on an alternate earth) and brought back to Mars. Sure enough, after Hell commences its invasion of Mars, the Doom Marine awakens as bloody-minded as ever. He then arms himself with a pistol, reclaims his Praetor Suit and begins to fight the hordes of hell once more. After he saves Earth, he is captured by Hayden and put into stasis again, while the scientist prepared his next plans.

With regards to Quake canon, Champions games is a prequel to the Arena games (Quake III Arena/Live). Though with regards to when the Doom Marine was pulled into the Arena Eternal are roughly switched chronologically. That is that Doom Slayer entered into the Arena Eternal during the earlier Champions competition, whereas an earlier incarnation code-named "Doom" entered in the later Arena competitions.

DOOM (1993)/Thy Flesh Consumed
B.J. and his squad is sent to Phobos base after the UAC's teleportation experiments go wrong and hell breaks loose on Mars' moons. A team including Doomguy go to check it out, but due to a demonic invasion, everyone but Doomguy dies, so it's up to him to take care of business. Doomguy takes the fight through a portal to Hell where he defeats the Spider Mastermind and returns to Earth. Upon returning to Earth, Doomguy finds it already ravaged by demons, who decapitated his pet bunny, Daisy. He fights the forces of hell the Spider Master Mind had sent through ahead and takes revenge for his dead pet.

Doomguy continued to keep a lucky rabbit's foot taken from Daisy upon him.

He has since gotten a new, much living Daisy.

DOOM II/No Rest for the Living/Final Doom
After the battle on Mars, Doom Marine takes leave and returns to Earth, only to discover it has been invaded.

The survivors plan to flee the planet, but the only remaining functional spaceport is under Hell's control. He fights to take back the spaceport and the remaining humans succeed in fleeing to space. Doomguy (or another Marine character who returned to Earth directly from Mars) then travels to the Demons' entry portal on Earth to close it and succeeds after killing the Icon of Sin. Humanity then returns to Earth to rebuild.

Final Doom covers the Doom Marine's (or possibly another character Marine Commander's or characters) destruction of two other Icons of Sin, one after Hell's invasion of Jupiter's moon Io (TNT: Evilution) and the other after another invasion of Earth (The Plutonia Experiment), both invasions being brought about by further experimentation with interdimensional gateways.

Doom 3 (in Relation to Doom/Doom II/Final Doom/Doom 64)
Doom (2016)'s timeline is built largely on the framework of the Doom 3 timeline (see shared timeline), while it's known that Classic Doom's timeline is also somehow part of the timeline as well (although its exact placement is not known and has been placed anywhere between 21st and 22nd century).

Doom II Intro/Doom 3 (note the exact order is not known and is dependent on if Doom 3 is a prequel to Doom or a sequel to Doom). If classic Doom series takes place in the 21st century (a century before Doom 3) or in the 22nd century (presumably after Doom 3, or at least co-currently), its not specific (but sources may give clues). Quake Champions 'lore' appears to suggest that Doom 3 was hero's first time to Mars, and thus making it a prequel to Doom 1-3:


 * Recently transferred to Mars, this soldier got more than he asked for when Dr. Betruger betrayed the UAC.


 * PDA: Given to you on your first day on Mars. Allows you to read other people's email and hear their personal recordings.

Doomguy is sent to Mars, and as stated in the Doom manual (much as in Doom 3). Doomguy is taken out of normal duty and shipped to Mars to assist the UAC after assaulting a senior officer for ordering him to engage civilians.

According to the Doom II manual, he stops an invasion of Mars Base on the red planet (much as in Doom 3), later heads to earth in a drop pod (just before the events of Doom II).

However Doom II's marine may or may not be the same character or a separate character as the Doom I character depending on different manuals and websites (see Marine (Doom II)), and characters from Final Doom may be different as well (see Marine Commander). His backstory differs from that of the original Doom character in that he fought on UAC Mars Base and escaped in a drop-ship (mirroring events of Doom 3, and even Doom RPG). Whereas original Doom character fought in Phobos and Mars and in both original Doom and Ultimate Doom reaches earth via transporter gateways. If taken into consideration the backstory to Doom II might actually be the same events of Doom 3 (placing Doom II after Doom III in the 22nd century essentially).

Some interviews (and the 'about description on the 2020's release of Doom 64) suggest that Doom 64 takes place directly after Doom II (thus making Final Doom hero/heroes likely different marine/s). Quake Champions ties all the doom guys together including Doom 3's version, giving lore related to each one for the Doom Slayer character.

Doom Slayer has the Soul Cube he had back in Doom 3 (previously in the Hands of Olivia in Doom (2016) in his Fortress of Doom. This artifact can also be seen in depictions on a tablet in Kadingir Sanctum (along with many other tablets dipicting the Doom Slayer and his history/noteable events against Hell's forces) in Doom (2016). The Artifact is known as Artifact U1, the statue of Praetor suit found in Doom (2016) is known as Artifact U9, and both were found in Site 3.

Among the artifacts encountered in Doom 3 is broken remains of an outer Sarcophagus along with a broken stelae  discussing an 'ancient great Hero'. Upon closer look at the stelae its clear that the image is of the Classic Doom Marine, from the box cover of Doom 1. The same/similar image is found on an ancient manuscript in Doom 2016. The story as told from ancient documents being researched in the game is very close to the same story of the Doom Slayer from the Slayer Testaments. Also, nearby the stelae are what appears to be an image of a creature very similar to the Mother Demon/sister Ressurector the creature/creatures ancient Hero fought before he was sealed away. There is also mention of a demon that is said to have given birth to all other demons in an audio log. These plot points appear to be heavily influenced by each other.

See Doom Retcon Timeline (ID multiverse timeline (Doom 3 as a prequel)) & Doom Timeline (ID multiverse timeline (Doom 3 as sequel)) for alternate interpretations of classic doom timeline...

How the Doom Slayer travels through Worlds and Time might be the least important aspect of his history. Just that roughly all the games appear to take place in a single 'earth' timeline in some fashion or other. Parallel earth have not yet been confirmed in Doom series itself, though possibly hinted at in the Art of Doom Eternal (although its part of Quake Champions', and MachineGames universe's stories, see Young Blood (B.J. mentions having traveled to or seen several Earth dimensions)).

DOOM 64/Lost Levels
Something survived on Mars' moon, however. The Mother Demon works to resurrect the fallen armies of Hell. Doomguy returns to Mars to take out the trash, journeys into hell again and kills the Mother Demon. This time, however, he closes the portal from the inside. He has decided to remain in Hell to keep the demons from ever escaping it again.

The sister Resurrector takes revenge on the Marine, by sending him away back to Earth, and attempts to kill him. He fights his way through another UAC base, works his way back into Hell, and takes revenge on the sister. He decides once again to find a perpetual and eternal path through DOOM, slaying more demons of hell.... (note the quote from the Lost Levels ending is based upon a similar quote in the Slayer's Testament, and intentional link between the two games stories)

Pre-DOOM 2016
In the time of King Novik, as the Argenta secured peace and safety through dimensions across time and space, Doomguy is found by the Night Sentinels in a valley outside the castle walls on Sentinel Prime. How he arrived is unknown. Sentinel scouts had found the Outlander bloodied, clawed and near death, mumbling of impending Doom and the forces of Darkness. The scent of blood followed him, and the gore that stained his armor seemed not entirely of his own. By Argenta law, he would be judged in the Coliseum, where he would be given the chance of all who stray from the Path to fight for his freedom.

His mind seemed crippled with rage. His will overcame his injuries, and in the Blood Arena, he proved his worth. His technique was crude and brutal, but the determination in his charge echoed that of any trueborn Sentinel. His war cry echoed through the Coliseum as did the sound of his fury, and the guards cheered his banner, 'Rip and Tear' they shouted as the beast pushed beyond mortal wounds and certain death.

He would be gifted no rank, no title. The survivors in the Arena were provided only one reward - the right to earn an honorable death while spreading the blessings of the Maykrs to those in need.

Doomguy's determination was witnessed, his ravings documented, and through the word of the Order, Deag the Khan Maykr had him brought before her. She set her minions to learning his tongue, for with his ugly words he spoke of lands unseen, creatures born of fire and a dark place unknown to the Queen and her cast. Yet another opportunity to expand the gift of the Maykrs to those in need.

On the eve of the Black Star, the Dark Ones came from a world beneath our own, not through ship nor ephemeral vessel but through the fabric of dimensions. Out of swirling, fiery gates came horned beasts from a timeless realm. First one, then many, crashing waves of evil swelled from the obsidian forest of the Argentian Overlands. The Alorum clans from the eastern mountains fell first to the black hordes of devils, and the city of Telorum was slung under the weight of their charge.

He and the Sentinels rose to meet the beasts with a spear in hand, the might of the holy fleet striking back at the demons, but the dark gates from whence they came gave birth still to even greater hordes.

A line of blood was drawn with the fallen on both sides, and the Unholy Wars began as the time of darkness came upon us, thus beginning the first age. In the 1st Age, Hell constantly strove to take over Argent D'Nur in order to harness sentinel energy and expand their dominion.

The Crowned leader of the Night Sentinels loses his son on the battlefield. In return for his offspring's revival, he betrays the Sentinels and the city by guiding the traitorous Deag Grav to the Wraiths. The Hell priests put a curse on their patron deities to siphon their homeworlds energy. To which (in a secret deal forged between the Maykrs and Doom overlords) would blend Sentinel Energy with demonic essence in conjugation with the tormented souls of the fallen Argenta to produce the more powerful Argent Energy.

Valen's son was returned to him, but in a twist to their bargain had instead been resurrected as the Icon of Sin.

The demonized former sentinel tears the Argent City apart while everyone watched helplessly. To make matters worse, the Slayer and his contingent of Sentinel warriors ventured deep into the heart of Hell itself in order to bring the fight to their enemies' heartland.

Only for the noble warrior creed to find out the horrible truth behind the secret of Argent Energy. Not only was the fuel source utilized by the Argenten people fueled by the suffering and defilement of their fallen brethren; whose corpses were later transformed into legions of the damned after they're souls had been processed.

The Order soon realized they had been betrayed from within by the Argenten people's very patron divinity; the Kahn Maker. It is revealed she had in fact helped construct the malignant devices which the Legions of the Doomed used to harvest the souls of their enemies, the slayer's people, her subjects.

In order to process and refine their tormented souls and concentrate their inherent quintessence into refined Argent Energy. After they'ed returned to their homeworld to convey such a horrendous finding, the Night Sentinels found themselves rejected by their former capital. As the Deag; now going by the moniker of Hell Priests, corrupted by their exposure to demonic essence and the influence of the Kahn Maykr. Had turned Sentinel society against those who knew the awful truth.

Wronged, betrayed and consumed with rage, seeking vengeance, retribution, and redemption, the Slayer decides to reenact his murderous crusade on Hell alongside the resistance sect known as The Loyalists. Samur Makyr, also known as the Seraphim, would spirit him away from prying eyes in order to give him immense power (in Christian mythology, a Seraphim is the highest rank an angel can achieve).

In the time that followed, however, another great Titan had been dispatched by the armies of Doom to waylay another Argenta city heralded by the Night Sentinels.

In an epic battle that waged for an untold period; the Doomslayer would rise to the occasion wielding his own Crucible Sword and strike the towering behemoth down. In awe of the foreigner's might and menace; the people of Argent D'Nur crowned him as their latest king, inaugurating their savior with the moniker of the Doom Slayer. While trapped in Hell by yet another betrayal from the Hell Priests, an entity known only as "The Wretch" would seek the Doom Slayer out. He would enhance his armor into the Praetor Suit so that the Slayer can better survive in Hell with his newly obtained inhuman powers. As time may flow differently in this dimension, the Doom Slayer torments Hell for thousands of years long after the remnants of his Loyalist sect died out.

The demons, unable to defeat him, instead devise a way to contain him. After being lured into a trap at Kadingir Sanctum, he is captured by the forces of Hell, separated from his Praetor Suit, and trapped in a sarcophagus, sealed by demonic power.

DOOM (2016)
Samuel Hayden retrieved the Doom Slayer from Hell in case the demonic forces escaped onto Mars, which they did. He awakened him to stop a demonic invasion of Mars instigated by his former protege, Dr. Olivia Pierce. He is released from the sarcophagus, supplied with his Praetor Suit, and sent to work. He journeys between worlds, destroying the Gore Nests that serve as Hell's links to our world. Samuel Hayden guides him through slaying the demons on Mars and Hell, equipping him with a dimensional tether allowing him to travel between them. The Doom Slayer, disapproving of Hayden's deadly Hell energy-siphoning operations, destroyed the Argent Energy filters he asked him to carefully remove. The Doom Slayer eventually retrieved the Crucible, used it to free the Wraiths from their subjugation and absorb their Argent Energy, and killed Olivia Pierce. Then Hayden uses the tether to return the Slayer to him, incapacitate him, and take the Crucible from him. Hayden explains that even though his attempts to siphon energy from Hell resulted in a massive loss of life, he believes the massive energy crisis on Earth it's solving makes the ends justify the means. He claims that even though the Slayer destroyed the filters, he can rebuild his operation with the Crucible, which he reveals to be a long blade of pure Argent Energy. To prevent the Doom Slayer from trying to stop him, Samuel uses the tether to send him to a place where he can do no harm and where no harm will come to him.

Quake III Arena/Quake Champions
The Doom Slayer is sent to the Arena Eternal, a series of battlegrounds where the Vadrigar have taken the greatest warriors from across time and space, and even parallel universes, to kill each other in endless gladiatorial combat for their amusement. Every time the gladiators are fragged in combat, the Vadrigar revive them so they may fight again. In Quake canon, Champions is a prequel to Arena.

The background of the Slayer in Quake Champions includes lore taken from Doom (2016), Doom Classic/Doom II/Doom 64, Doom 3, and the original Quake Arena games.

DOOM Eternal
The demons have invaded and devastated the Earth, just as they did in Doom II. After traveling to Earth from the Fortress of Doom in orbit, the Doom Slayer must use his upgraded Praetor Suit and Super Shotgun and a wide range of weapons both old and new to stop them.

It is confirmed that Doom Slayer is one of the generals of the Night Sentinels and human whereas the rest of the Night Sentinels are of the Argenta race. In the distant past, after leading a successful battle against the demons of the Blinded Order, his army was killed by a group of demonic dragons. As he was about to be killed after a dragon tossed him into the air and he fell thousands of feet below, he was rescued by the Seraphim.

During the betrayal of the Valen, the Doom Slayer led the remnants of the Night Sentinels that were still loyal to his cause to destroy the foundry of souls, the source of the Kahn Maykr's power to turn the tide of the war against the forces of Hell and the corrupt Argenta. Deag Grav eventually trapped and stranded the Slayer and his warriors in the void.

It is revealed in flashbacks that after being found by the Night Sentinel patrols, he was brought to their arena on Sentinel Prime to be judged whether he is worthy to be a warrior of the realm or not by Ranak and Grav. He eventually succeeded in proving his worth and under the order of the Khan Maykr, he was made into a Night Sentinel, eventually becoming one of their warrior-kings.

Due to his exploits in exterminating demon hordes on Earth, most people regard him as humanity's avenging angel and savior while the UAC and Allied Nations try their best to deny his existence. The resistance refers to him as the Doom Slayer and sometimes the Doomguy.

Powers and Abilities
Though it is only told by demonic recordings, the Doom Marine had managed to kill Hell's greatest Champion 'The Titan', indicating how powerful he is and how he became the most feared to be to Hell's Legions.
 * Badass Incarnate: Having become an icon in gaming, and battling the forces of Hell from decades to eons, has earned the Doom Marine the status of being an absolute badass. This makes him an invincible and unstoppable force to be reckoned with.
 * Transcendent Human Physiology: The Khan Maykr states that the Doom Slayer was once a mortal so it is safe to say that the blessing of the Seraphim has transcended him to become something more than a mere human.  Despite fighting with demons for decades Doom Marine did not grow old or lose any of his strengths also no longer needs food, drink or even rest, becoming something akin to an immortal.
 * Immense Physical Condition: Despite being human, the Doom Marine has shown to possess immense physical strength, durability, endurance, speed, stamina, and superior agility and reflexes. He outmaneuvers his opponents with great dexterity, avoiding their attacks, and yet is capable of enduring the hits that the Demons are able to land. His strength is sufficient to grapple and overpower superhumanly strong demons in hand-to-hand combat, and perform visceral "Glory Kills" to ensure their complete destruction. After the blessing of The Sepharim he gained even greater power matched only by his own will, greatly empowering him to even more impressive levels. These abilities are all further augmented by the Doom Marine's Praetor Suit and are used when fighting against the forces of Heaven and Hell.
 * Indomitable Will: The Doom Marine posses tremendous willpower and determination which cannot be weakened. No matter the situation, opponents or obstacles he pushes forward, refusing to give up regardless of what happened. His determination to wipe out demons and protect humanity has remained with him constantly for years.
 * Intimidation: Due to his appearance acts and rumors, the Slayer is greatly feared among mankind even though he never injures or kills any of them. The ARC soldiers were terrified when he came before them. Despite most demons in battle are not frightened by his presence and attack him constantly; the lore entries show that all of Hell itself is terrified by the Doom Marine to an extent that they fought vigorously just to keep him sealed in his tomb when a UAC excursion team came looking for him. The Hell Priests and even Khan Maykr are also greatly terrified of him as well.
 * Destruction Empowerment: The most unique thing about the Doom Marine is his ability to grow stronger and become even more tenacious with every demon he kills. According to the game's lore, this is the result of Samur Maykr giving the Slayer the ability to absorb the souls of those he killed.
 * Argent Energy Absorption: The Doom Slayer can absorb and metabolize Argent Energy via his Praetor Suit, which reroutes it throughout said combat fatigues subsystems and into his body. This allows him to increase either his Health, Armour or Ammo to maximum levels.
 * Rune Absorption and Usage: Through some unknown means, the Slayer is able to use mystic runes that he gains upon completing trials. Once a trial is complete, the Marine can then use a rune to gain new abilities.
 * Powerup Usage: Whereas powerups (such as Berserk and Haste) in the game are described as killing or driving human users mad, the Hell Walker can use these without any trouble, sustaining full control and not taking any damage to either his body or mind from using such artifacts multiple times.
 * Expert Combatant: The Unchained Predator is a highly trained and experienced combatant, even when lacking ammo and weapons, he can slay demons just with his bare hands alone, without the need of any melee weapon, he can defeat and tear apart demons far bigger and stronger than him just with his own skills in hand-to-hand combat. Thanks to training with the Night Sentinels he became quite disciplined and became able to focus his rage and became proficient with swords and spears. With the Praetor suit, these skills are further increased, making him a monster in both armed and unarmed combat. In his stronghold, he has his own special room where he can summons demons to still maintain and improve his combat abilities.
 * Weapon Mastery: The Doom Marine is capable of using any weapon or firearm in his possession with master proficiency. He can use all artillery he comes across with great effect, while also upgrading and modifying his arsenal. He is also capable of carrying a vast amount of weapons, carrying up to 12 weapons including special weapons (Chainsaw and BFG) and grenades. Also able to use swords and other bladed weaponry equally effectively due to his training and crusades with the Night Sentinels.
 * Advanced Intellect: Due to his time spent in a technologically advanced civilization, the Slayer is able to use technology from other worlds with no signs of unfamiliarity, despite resorting to violence. He is also an adept study of computer sciences as the lore of Doom Eternal, as well as literary paraphernalia within the Fortress suggests, that after uploading VEGA's core memory into the Maykr/Argenten stronghold. That the Marine had been keeping up in maintaining its system functionality; showing a keen tech-savviness belying his otherwise brutish approach. He also improves his Praetor suit with the help of VEGA as well as creating his own ballista and training room for training.

Praetor Suit
This armor has carried the Doom Slayer through untold horrors. Not even the fires of Hell can stop his advance.

Attachments

 * Deep Space Rebreather: Automatically regulates the air mixture for high and low-pressure environments.
 * High Impact Chest: Snaps into place on the chest to protect the wearer from high impacts.
 * Performance: Created for the Praetor Suit to maneuver effortlessly while in the air or in a vacuum.
 * Stabilizers: Helps the wearer to adjust movement while in the air.
 * Delta Jump-Boots: This early version of the Delta V Jump-Boots was not nearly as compact as the finished model, but the extra mass was still used to adjust movement in the air.

Arena
Though bare-bones, this early armor fits like a glove.

Attachment

 * Helmet Multi-Tool: Multi-tool with laser sighting and headlamp.
 * Shell Holder: Protect the shoulders from damage and demon blood.
 * Arm Bandages: Lots of demons require lots of shells. Shotgun ammo should be always on hand.
 * Thigh plates: Trade carrying space for increased protection.
 * Combat Knife: Used for last-ditch efforts.

Doom Marine
Recently transferred to Mars, this soldier got more than he asked for when Dr. Betruger betrayed the UAC.

Attachments

 * No Helmet: The standard-issue space marine helmet is airtight and durable, while still allowing a wide view area.
 * Flashlight: Pierce the darkness using this high-powered flashlight. Unfortunately, it is quite large and is almost impossible to use while firing.
 * Spare Mags: Keep ammo close at hand. You're going to need it.
 * Air Tanks: Doesn't offer additional protection but allows demons to see their death in your eyes.
 * PDA: Given to you on your first day on Mars. Allows you to read other people's email and hear their personal recordings.

Doom Guy
The original and iconic armor. It forever changed the world.

Attachments
Praetor Suit 2.0
 * Classic Face: Relive the old days using the face you know so well.
 * Down But Not Out: Bruised, beaten, and bloody. This is where the fun starts.
 * Advanced Helmet: A more sophisticated version of the base helmet.
 * Bandolier: Ready for war.
 * Arm Guards: For when fighting demons gets nasty.
 * Abdominal Plating: For when you need to hide your abs.
 * Leg Armor: Thick plating for the upper legs.
 * UAC Riot Greaves: Protects the shins from heavy impacts.
 * Spare Shells: Keeps shells handy in case of an emergency.

This armor augmented via VEGA and slayer himself is now better and stronger than ever with more exclusive equipment and other suitable things.
 * Retractable Blade: Slayer now has a blade on his left arm which ejects out during Glory kill
 * Additional Flag Granade: On slayer left shoulder now carry launcher capable to shout out grenades, ice or flamethrower
 * Delta Jump-Boots 2.0: Slayer carry boots which allows him to perform double jump while leaving him to adjust movement in the air.
 * Dash trusts: thanks to trusters Slayer now can move very swift on both to ground and air.

El Diablo Shotgun
This alternative to the Super Shotgun is engraved with the images of its victims. Well, after their skin was boiled off.

Doom 2 Shotgun
The DOOM 2 break-action double-barrel Super Shotgun has been to Hell and back. It's old, beaten, and packs a mean punch.

Character Skins
Doom Eternal introduces a number of unlockable character skins for the Doom Slayer. While the majority of the player skins can be unlocked during normal gameplay, some are only available through DLC, external promotions or the Slayer's Club. For example, the Doomicorn, Purple Pony and Night-mare skins are only available as part of a time-limited Twitch Prime promotion.

Trivia

 * In Doom (2016), the Slayer fist bumps his Doomguy counterpart when it is collected, a special animation not shown with any other collectible figure.
 * In Doom Eternal, he again has a special interaction with his toy counterpart. In this case, he extends his Doomblade and flicks up the arm of the toy to match it.

Behind the scenes
"Doom Slayer" is the main official title for this character in Doom (2016), Doom Eternal, and Quake Champions and is the title used for the Slayer's Testaments.

The title "Doom Marine" or "DOOM Marine" first appears as a title for the main player character appears in earlier material including the Doom RPG website, and the introduction to the Doom 3: BFG Edition manual.


 * Step into the boots of DOOM Marine and experience his adventures for the first time, or all over again. Featuring enhanced versions of DOOM 3, DOOM 3: Resurrection of Evil and the all-new DOOM 3: The Lost Mission, plus the classics DOOM and DOOM II, DOOM 3 BFG Edition is the consummate DOOM experience.


 * Doom RPG is a first-person turn-based role-playing game set in the Doom universe. Developed specifically for your mobile device, you reprise the role of the Doom Marine made famous in the groundbreaking id Software titles Doom, Doom II, and Doom 3. Say goodbye to humdrum mobile gaming and prepare yourself for the return to Mars in a showdown with the legions of Hell!

Doom Slayer owns a book about Daisy (presumably one he wrote himself). He also owns a biography about Flynn Taggart and plenty of comics from Taggart Comics Group. He also signs into his computer as FLYNNTAGGART, but whether or not it means anything, either a previous user of the computer or his own credentials (his name or alias), is anybody's guess...

He also has the Soul Cube (2016) in his collection as a nod to the Doom Marine from Doom 3.