Doom Slayer's History
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.
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 has 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.
The demons have invaded and devastated the Earth, just as they did in Doom 2. 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 he is human whereas the rest of the Night Sentinels are of different blood. 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 remnant of the Night Sentinels 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 the flashback that after being found by the Night Sentinel patrols, he was brought in the arena to be judged if 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 Makyr, he was made into a Night Sentinel and became their general later on.
Due to his exploit in exterminating demon hordes on Earth, most people regard him as the avenging angel and savior while the UAC and Allied Nations try their best to deny his existence, referring to him as The Doom Slayer and sometimes The Doomguy. At some point, B.J. became stranded in Sentinel Prime on Argent D'Nur after remaining in Hell. There he is captured by the Night Sentinels and ended up in a different dimension.
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 depicting his Praetor Suit), and the Chamber of the Hero. Still, the martian civilization 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.