Dark Lord

Dark Lord is the title of the supreme ruler of the realm of Hell. The title appears to refer to any entity which claims dominion over Hell, with the realm's past being divided into "ages" based on the reign of these creatures.

Davoth
"You bring violence and war to the Dark Realm, but conflict was born in Hell. It is inevitable... a fire that fuels creation and gives purpose where there is none. Stand and fight, Slayer. Honor your true God. Fight and show me your purpose."

- The Dark Lord to The Doom Slayer

According to Maykr history, the original Dark Lord was an immortal being once known as Davoth, created by The Father to rule over his first deliberate creation, a realm called Jekkad. Jekkad was a higher plane than even The Father's first creation, Urdak, and Davoth was a Primeval, one of the first gods, created to rule over it.

The people of Jekkad made many great wonders, seeking to make their land a paradise: The Father had filled them with ambition and granted them a lack of restraint, wishing to see them excel in all things. They were long-lived, but not immortal like the Maykr of Urdak, and it was in this single flaw that the seed of Hell itself was planted.

The Father created Davoth with an undying love for his people and a desire to better their lot, and both he and the denizens of his realm came to regard mortality as a curse. Davoth knew that he himself was not mortal, and feared the possibility of his beloved people's extinction, leaving him alone in an empty realm. Turning their intellects to defeating death itself, and without self-doubt to reign them in, the people of Jekkad, guided by Davoth, commenced their search.

The Father saw the future of this endeavor, that Davoth and his people would never cease in their search, regardless of the cost. Foreseeing that someday this ambition would threaten all creation and that Davoth would someday seek to challenge The Father himself, The Father sealed off Jekkad from all other realms.

Davoth saw this act as an unforgivable betrayal by his creator, directing his fury at the barriers that encircled his domain as his people continued to fall to mortality. He became The Father's nemesis, the Dark Lord, while his realm would come to be known as "Hell" to the people of Urdak. The once grand and beautiful realm fell into horror and ruin as its denizens set aside all other concerns save for their singular purpose.

Davoth continued to test at the boundaries of his prison, with his legions spilling forth into other realms, defeating many forces sent by The Father to stop them. With each victory, the Primeval's power grew greater. Finally, moved to act, The Father entered the despoiled realm and, atop the Pyramid of the Lost, once a temple to The Father, he tore the essence from the Dark Lord's body and cast it down. While Samur Maykr begged The Father to destroy the Life Sphere containing Davoth's essence, he refused, as Davoth was still his own creation: instead, he placed the Sphere in the Temple of Souls.

While Davoth was reduced to nothing but a sphere containing his essence, he continued to whisper his influence to the corrupted people of his realm. Ultimately, he would be restored to a physical body by the Doom Slayer through the use of the Maykr device known as the Luminarium, as part of the latter's plan to destroy the Primeval and in doing so Hell itself. It is stated by the intern that the only way to truly destroy the Dark Lord and by extension Hell was to restore his physical form and kill him. When resurrected, he appeared in the form of the Slayer. The Slayer tried to execute him there and then, but Davoth informed the Slayer that no blood can be spilled in the Luminarium. Davoth told the Doom Slayer that he would be waiting in the city of Immora. The intern would later inform the Doom Slayer that should he destroy Davoth, every demon outside of Hell would be destroyed.

When the Slayer arrived at Immora, Davoth, clad in a red-colored mech, greeted him with his entire demon horde. As the remaining forces of Argent D'Nur rose to aid the Slayer, and the Slayer advanced into the city of Immora, Davoth retreated into his chambers, where he goaded the Slayer into fighting to show him his “purpose.”

During the fight, Davoth and the Doom Slayer were transported across realms conquered by the forces of Hell. In the ruins of a city on Earth, Davoth demanded that The Father tell the Doom Slayer the truth - that Davoth was the true first being, responsible for all of creation, and that The Father was his creation. The Father betrayed Davoth, sealing him away in Jekkad and stealing his power of creation. In revenge, Davoth swore he would unmake everything by his hand, as he had made them. He influenced Samur Maykr into placing Doomguy into the Divinity Machine, with the intention of having the Slayer unconsciously contribute to the destruction of the Maykrs and The Father.

After defeating Davoth, the Slayer removed his helmet and approached him slowly. Davoth asked if the Slayer had anything to say to his creator before he struck him down. Slayer stabbed Davoth with the Doomblade, uttering only one simple word, “No.” Davoth's Life Sphere ejected from his body and exploded. As a result, every demon outside of Hell was instantly destroyed, and the Doom Slayer collapsed, having become a resident of Hell through the years of his long crusade, yet not enough to die. His comatose body was entombed where the life spheres of Davoth and The Father's had been kept - the Temple Of Souls.

Later Dark Lords
Following Davoth's near-destruction, it appears that other powerful demons within Hell vied for his former rank and appointed themselves as Dark Lord in his place.

Given the chronology of events, it appears to have been Davoth's successor, the Dark Lord of the First Age, who made a pact with the Khan Maykr allowing for the construction of "Soul Spires" in Hell. These structures, including the Citadel located in the Hell-city of Nekravol, fused mortal souls with Hell energy to form Argent Energy, an incredible power source which the Maykr could use to stave off their degradation following the loss of The Father. In return for allowing the construction of the towers, Hell would be provided new worlds to harvest, as well as the refuse from the soul extraction process, husk-bodies which would transform into demons much more quickly than if the process proceeded normally.

A voice identified as the current Dark Lord (presumably of the Fourth Age ) was heard contacting Olivia Pierce. This is implied to have been the Spider Mastermind, which was later destroyed by the Doom Slayer.

Quotes

 * "NOOOOOOOOOOOOOOOOOOOOOOO!" -Davoth after the Khan Maykr died.
 * "You feel you are prepared now, for this..." -Davoth as a lifesphere taunting the Slayer.
 * "No blood can be spilled in this holy place. Our time will come. If you survive, I will be waiting in the city of Immora." -Davoth after deflecting the Slayer's buckshot.
 * "Aten Me." -Davoth summoning his army to destroy the Slayer.
 * "You bring violence and war to the Dark Realm, but conflict was born in Hell. It is inevitable... a fire that fuels creation and gives purpose where there is none. Stand and fight, Slayer. Honor your true God. Fight and show me your purpose." -Davoth beginning combat with the Slayer.
 * "I will bathe in your blood!" -One of Davoth's threats toward the Slayer.
 * "You will burn!" -Another one of Davoth's threats.
 * "Die, Slayer!" -Another one of Davoth's threats.
 * "You cannot stop me!" -Davoth taunting the Slayer.
 * "For too long have I been imprisoned by my own creations. You will not stop me, nor the one who betrayed me. Tell him. (He was the first being, and my creator. As he fell, I ascended.) They lied to you, Slayer. Immora and its people would have been perfect if not for the treachery of my servants. They sealed me away, stole my power and name, and now the time has come for a reckoning. As all things have been made by my hand, so shall they be unmade. Starting with you." -Davoth tells the Slayer about being the true Father.
 * "I will devour your soul!" -Davoth threatening the Slayer one last time.
 * "Tell me... have you nothing to say to your creator... before you strike him down?" -Davoth's last words.

Trivia

 * The voice that calls out "NOOOOOO!" after the death of the Khan Maykr in Doom Eternal is identified as "Dark Lord" in the game files, but was originally only identified as "Mysterious Voice" in the game itself. After the release of The Ancient Gods - Part One, this was changed to match the game files.
 * It is possible that the Slayer is the parallel universe counterpart of Davoth since Jekkad was a regular realm before. That's why they look identical.