The Night Sentinels, first mentioned in Doom (2016) and later encountered in Doom Eternal, were the military force of Sentinel Prime, who acted as guardians of the City of Argent D'Nur and of the Wraiths prior to their civilization's fall to the forces of Hell. They appeared as technologically advanced knights wearing powered suits of white armor and primarily attacked with sword- and spear-like weapons. According to the lord of the Fourth Age of Hell, the Doom Slayer "wore the crown" of the Night Sentinels, and thus may have been considered their leader.
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 powerful force with which to be reckoned.
The Time of Grief
In a period known as the Time of Grief, during the rule of King Etrex, the Argenta first made contact with the Maykrs, who brought many gifts to Argent D'Nur and sought to ally with its people. The Argenta were astounded by their magnificent technology, and were soon convinced that the Maykrs were gods. Although the Wraiths were still venerated, they were placed into a deep slumber in the Elemental Sepulchre to prevent their power from becoming uncontrollable.
In time, the Argenta spread out from Argent D'Nur using the machines and magic of the Maykrs into what they called the Empyrean Void - evidently what is otherwise known as outer space, from its depiction in illustrations. They sought to spread the word of the Khan Maykr, which at that time they considered to be enlightened. In this process they made contact with many worlds and peoples previously unknown to them and made many alliances.
After a time, the Khan Maykr spoke to the king of a warrior who would cause a schism among the Argenta, claiming that only a holy rite with one of the Maykrs' own machines would be able to expose him. This "Divinity Machine" would cleanse his impurity and ensure the prosperity of the Argenta.
Coming of the Outlander
During the reign of King Novik, a strange outlander was found badly injured and near death, ranting about "impending doom and the forces of darkness" in a foreign tongue and covered in blood that was not wholly his own. Following the Argenta traditions, he was taken to their Coliseum to be offered the chance to fight for his freedom in a trial by combat. In spite of his wounds, the stranger fought with surprising ferocity, sheer stubbornness keeping him from succumbing to his injuries. Though victorious, his only reward would be a chance to die honorably fighting the enemies of the Argenta. The Khan Maykr, on the other hand, was more intrigued by the dark realms the stranger spoke of, seeing it as another land for the Maykrs to enlighten.
The First Demonic Invasion
Not long afterwards, the first reports of demonic invasion arrived, with the Eastern mountains of the Alorum being first to fall. The Argenta and Maykrs alike were baffled by this mysterious new enemy.
It was the Order of the Deag that discovered the secrets of the Hell essence that the demons used as an energy source. The Argenta were soon able to utilize this force for themselves, allowing them and their Maykr allies to devise new weapons and drive back the invaders. Though some of the Night Sentinels voiced suspicion over the nature of the essence, the people soon grew dependent on its use.
Meanwhile, the outlander's prowess had earned him the unprecedented merit of being made a Night Sentinel himself; his reputation, as well as his hatred of the demons, made him both a powerful weapon and a valuable ally. To defeat a mighty Titan, the outlander was taken to the Temple of Purity by Samur Maykr, the chancellor to the Khan Maykr also known as the Seraphim. Acting without the consent of the Khan Maykr, Samur subjected him to the Divinity Machine, granting the outlander incredible power. Taking a Crucible as his weapon, he killed the Titan and became known as the "Doom Slayer". Strangely, the Khan Maykr did not seem upset by her servant's disobedience, though he vanished soon afterwards.
Unknown to the Argenta, the Khan Maykr had begun construction of secret factories in Hell, sending her servants to negotiate with the demons to allow them safe passage. All this would be exposed during a mission where it was discovered that the Essence the Argenta used was derived from the souls of their dead. To their horror, the Night Sentinels saw that the monstrous factories where the dead were rendered into raw material were built with their own technology as well as that of the Maykrs', refining the Essence into Argent energy. In return for a share of the Argent energy produced to sustain their homeworld of Urdak, the Khan Maykr had agreed to grant the demons access to all the worlds under the Maykrs' influence - an unholy alliance between Heaven and Hell.
The Night Sentinels, loyal to King Novik, tried to warn their people of what they had seen, but were disbelieved and declared heretics. Argenta society soon became divided between the Ascended Empire devoted to the Maykrs and the Night Sentinels who remained loyal to their rightful king.
As the civil war continued, the Order of the Deag claimed they had found a chance to end the conflict. The Doom Slayer and the most valiant Night Sentinels would attack the infernal factories of Nekravol, cutting off the Argent energy supply from the demons and the Maykrs alike. When they entered the portals, they found the Deag had sealed the way back and realized they had been betrayed once more.
Fall of Argent D'Nur
Deag Grav, described by the demons as a "lowly Hell priest", was finally able to corrupt the Night Sentinel Commander Valen, who would come to be known as "the Betrayer". Valen had been tortured with horrific visions of his deceased son's suffering in Hell, and Deag Grav promised that he would be resurrected. In return, the Betrayer would lead the Hell priest and his forces to the Wraiths. Deag Grav used the power of the Crucible to destroy the Wraiths and forged a powerful source of Argent energy, known as the Well, from their souls. This began a new period in Hell known as the Ascension, and immediately led to the fall of Argent D'Nur in a massive attack. King Novik and the remaining loyal elite of the Night Sentinels ultimately perished in a last stand against the demons. The only ones who survive among the Argenta now are those who continue to serve the Maykrs, and by extension the forces of Hell.
As repayment for his service, the Betrayer's son was indeed resurrected, but in the form of the Icon of Sin, who was then unleashed on Argent D'Nur to drag it into Hell.
It is unclear how many of the loyal Night Sentinels survived the fall of their civilization, but several are shown fighting alongside the Doom Slayer in a page from the Book of Daeva apparently after or during its fall. Accordingly, upon freeing the Crucible from the control of the demons, the Doom Slayer also releases five of the Sentinels' souls from captivity. Before the Slayer is tethered away by Samuel Hayden, the apparent leader of these spirits salutes the Slayer. Four of these spirits later reappear during the Slayer's sojourn through the remains of Argent D'Nur and assist him by leading him through the ruins to the resting places of the Wraiths, and finally to the location of Olivia Pierce.
Four sarcophagi almost identical to that in which the Doom Slayer was entombed can be found in the Advanced Research Complex shortly after leaving Samuel Hayden's office. The lids of these sarcophagi also bear the Slayer's mark, but in white rather than red. This suggests that the final followers of the Doom Slayer were entombed in much the same way as he had been, but that they did not survive their entombment and instead became captives of Hell until later freed, while the UAC later found their sarcophagi, now empty.
Statues of two Night Sentinels are kept by Samuel Hayden in his office. These statues depict the Sentinels as having carved the mark of the Doom Slayer into their armor as a sign of their allegiance to him.
The Night Sentinels who took the side of the Khan Maykr in the civil war would later be resurrected by a combination of Hell magic and Maykr technology, transforming them into the demons called the Marauders.
The Betrayer is known to have survived, remaining in Hell to fight the demons in the hope of atoning for his crime.
Several locations are associated with the Night Sentinels and the culture of Argent D'Nur:
- Argent D'Nur, the remains of what was apparently their capitol city, now absorbed into Hell. Also the original name of the world of the Argenta as a whole.
- Exultia, contains the castle of King Novik and the site of the transdimensional portal where the Deag priests trapped the Slayer and the Night Sentinels in Hell.
- The Gogolthan Ruins, a lost colony located in the Arctic region of Earth, where the Doom Hunter Base has been built over it.
- Hebeth, a hidden city located within the core of Mars that possesses a slipgate to Sentinel Prime.
- Sentinel Prime, seemingly a city itself and another name for the entire homeworld of the Night Sentinels.
- Taras Nabad, long-abandoned ruins of the holy city and royal palace which fell in the first attack by Hell.
- Three other names are seen on the Fortress of Doom's map of Sentinel Prime: Ardur, Kher Lodur, and Neras. Nothing is yet known about these locations.
The following locations are present in the 2016 multiplayer, and so are of ambiguous canonicity:
- Argent Breach, the long-abandoned tombs of fallen Night Sentinels.
- Empyrian, the destroyed floating remains of a temple to the Maykrs. Other damaged structures can be seen in the distance.
The Templar series of multiplayer armor pieces are based on the Night Sentinels' armor.