Night Sentinels

The Night Sentinels were an order of holy knights that protected the City of Argent and once stood against the armies of Hell in the realm of Argent D'Nur eons ago.

Background
They were the guardians of the Wraiths and acted as both their holy servants and a bridle for their awesome power.The Night Sentinels were imbued with Wraith energy and proved fierce opponents of Hell's legions, and according to the Ungmar Codex almost triumphed over Hell but were betrayed by a member of their order. The unnamed Betrayer struck a bargain with a lowly Hell priest, Daeg Grav, for the return of his son who had been lost in battle, 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.

Giant statues of the sentinels can be seen in Argent D'Nur, while two smaller statues labelled 'Ancient Sentinel' can be found in Samuel Hayden's office either side of a statue of the Praetor Suit.

Armor
The Night Sentinels' armor design bears some resemblance to the Praetor Suit, although their helmets resemble a crusader's great helm of the High Middle Ages.

Theories
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.


 * 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 simple have aided them in fending of 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.

They maybe based off the Spiritual Armor helmets from classic doom.

Trivia

 * Their armor is in Multiplayer as the Templar armor and its variants.