During the Sentinel Prime Civil War, the Night Sentinels were split into two factions: Loyalists and Order of the Deag. The Night Sentinels of the Order of the Deag will be enemies of the Doom Slayer in Doom Eternal.
According to passages from the Ligra Sultagenta, also known as the Book of Kings, the race of the Night Sentinels called themselves the Argenta. They arose on a world that was impaled by a giant impactor known as the Cosmic Spear, which unleashed the beings of immense power known as the Elemental Wraiths (also called the "Firstborn" by the Argenta), and began the evolution of life on their planet. They were driven by the hostile environment and the power of Wraithcall to take up arms and in time created a highly advanced warrior culture, defeating giant magical creatures known as the Ancestrals in order to secure their place in the world of Argent D'Nur.
They crowned a series of warrior kings, beginning with King Ormero the Father. All kings of the Argenta were required to be warriors and were expected to lead from the battlefield in times of war; those who could not were deemed unfit to rule.
The Order of the Deag was founded as a priesthood to tend to the Wraiths, which the people of Argent D'Nur both worshipped and feared. Through immersion in the Wraithcall, the people of Argent D'Nur mastered both magic and technology, and combined them. Together, these made the Night Sentinels, the core of the legions of the Argenta, a bulwark against the forces of Hell.
The Night Sentinels were formed by the first king of Sentinel Prime, Ormero the Father. They became the guardians of the Wraiths, and acted as both their holy servants and a bridle for their awesome power. However, due to the power of the Wraiths who could corrupt normal humans into monstrous beings, the Night Sentinels also acted as a control measure to the Wraiths to prevent their power from wreaking havoc.
These guardians were imbued with Wraith energy and proved fierce opponents to Hell's legions and, according to the Ungmar Codex, almost triumphed over Hell but were betrayed by a member of their order. The Betrayer struck a bargain with a lowly Hell priest, Deag Grav, for the return of his son who had fallen in battle, and he led the priest and his cabal to the source of the Night Sentinels' power, the Elemental Wraiths. Daeg Grav cursed the Wraiths while they slept, and the Hell priests stole their energy for their own devices. Argent D'Nur was defeated, and their realm absorbed by Hell, along with the Argent Energy that led to the creation of The Well.
The Night Sentinels adopt warrior culture and deems only the strongest warrior can rule Sentinel Prime. The King of the Sentinel Prime must be a warrior that can lead troops to battle not sitting behind the throne. Any kings who are unfit to lead troops will be disposed of and replaced with one that is more capable.
There are two factions within the Night Sentinels
- Loyalists: Night Sentinels who oppose Hell's Legion and the forces of the Khan Maykr.
- Order of the Deag: Night Sentinels who defected to the Khan Maykr side, they are opposed by the Loyalists.
Night Sentinels wield swords that can cut through demons with ease. In Doom Eternal, they wield a spear with Argent Energy as the tip.
- Marauders (Defected)
The Sentinels are somehow connected to the Doom Slayer, as their souls often act as his guide during his journey through Hell. While little is known for certain about the Night Sentinels, some have speculated that:
- The Doom Slayer was originally a member or perhaps leader of the order and is now the last of their kind. This is supported by the first part of the Slayer's Testament, which describes the Doom Slayer as wearing the "crown of the Night Sentinels."
- Others have suggested that they guide the Doom Slayer out of either respect for releasing the Wraith's souls, or out of having a mutual enemy in Hell's legions.
- Stone tablets and other "artifacts" in-game commonly depict the Doom Slayer and Night Sentinels fighting together, indicating that they have met before. The Doom Slayer's armor is very different, however, and he may simply have aided them in fending off the demon hordes.
Either way, the souls of the Night Sentinels appear to the Doom Slayer at various points throughout Hell to point the way or stand in solidarity with him.
- In Multiplayer, players can use the Templar Armor, the wearable equivalent of the Night Sentinel armor.
- The Armor that the Night Sentinels use is visually inspired by 15th Century Gothic Plate Armor, used by the Holy Roman Empire.
- Their Helmets are also inspired by the Great Helm, which was used by 13th - 16th Century European Knights.