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Warhammer 40K: Alpharius, Primarch of the XXth Legion

15 Minute Read
May 13 2024

Today we delve into the byzantine web of lies and deceit that is the Primarch Alpharius, master of the XXth Legion.

“Truth is so precious that she should always be attended by a bodyguard of lies.” ~Proverb, Old Albia, M.2


Alpharius Omegon (also known as the Last Primarch or the Lord of Serpents) was one of the twenty Primarchs created by the Emperor in the earliest days of the Imperium, just after the end of the Age of Strife. Like the other Primarchs, he was supposedly scattered from Terra by the Gods of Chaos and placed on a far-away world in an attempt to prevent the coming of the Age of the Imperium. In truth Alpharius Omegon are twins known as Alpharius and Omegon respectively, though they describe themselves as one soul in two bodies. While often considered the last Primarch to be discovered, he may have been the first. However according to Alpharius himself, this account is a lie.

Alpharius Omegon is an enigmatic figure within the history of the Legiones Astartes. No definitive record of his appearance and activities exist. There are claims that Alpha Legion Marines assumed his name and identity during wars and even council meetings with other Legions and Imperial officials, that Alpharius was somehow able to duplicate himself, and that he had a twin. Reports of his physical appearance seem to widely differ.


Secrets and Lies

It should be noted that the Alpha Legion‘s trademark secrecy extends to records of their Primarch. Little recorded information on his background exists, and almost all of what is currently known by the Imperium comes from the information provided by Inquisitor Kravin of the Ordo Malleus. Inquisitor Kravin was subsequently believed to have been tainted by the Alpha Legion and his current whereabouts are unknown. Hence, much of the Imperial data concerning the Primarch could be considered suspect, and indeed there are some who believe the whole Kravin affair was an Alpha Legion plot to plant misinformation in the Imperial records.

The greatest secret about the Alpha Legion Primarch is apparently told to none outside the Legion as unlike any of the other Primarchs, Alpharius has an identical twin: Omegon. It is unknown if the Emperor designed this, or was ever even aware of it. Upon their supposed reunion on Bar’Savor, the twins speculated that the Emperor may have kept their existences hidden from one another while it was equally possible they split into two beings while scattered in the Warp.

Alpharius and Omegon are both the Primarch of the Legion, although ‘Alpharius’ is the public face and appears as the more senior of the two. Though as both are identical it is possible for them to switch roles and have ‘Omegon’ play the public role. Supposedly from their first meeting and at least several times after, ‘Omegon’ appeared before the small court of Horus instead of Alpharius, that had appeared the last time to the court. They have been described as “one soul in two bodies” and collectively have been referred to as simply “Alpharius Omegon”.


Despite their close bond and describing themselves as two halves of the same soul, Omegon’s loyalties may not lie with his brothers (or vice-versa). During the Horus Heresy Omegon (or perhaps really Alpharius) took suspicious steps against his brother. This included sending troops on a suicide mission to destroy a Pylon array preventing the White Scars learning about Horus’ betrayal without his brothers apparent knowledge. Afterwards, an Alpha Legion fleet that may have been under Omegon’s command did not follow Horus’ orders to join with the White Scars, but instead seemingly provoked them into hostilities after blockading them long enough for Jaghatai Khan to receive a message from Rogal Dorn warning of Horus’ treachery.

As the Alpha Legion are known for schemes within schemes, the true nature of these acts may never be known. However, Alpharius and Omegon may not see completely eye to eye as the former is more accepting of civilian deaths than the latter. By the time of the Siege of Terra Omegon, posing as Alpharius, openly removed the Alpha Legion from the traitor war effort to take the Throneworld, though he offered a map of the Sol System‘s defenses as a parting gift.

Much of Alpharius’ history has been expanded upon in a tale given by the Primarch himself, which states that instead of being the last discovered he was instead the first and was raised upon Terra in secret. The tale is recounted in multiple places below, but despite being from Alpharius himself the Primarch states it is a lie.


Early History

Typical of the Alpha Legion’s own nature, conflicting tales of how Alpharius was rediscovered by the Imperium exist. Many of the tales have been proven lies, while many more still remain unproven or unknown. A dubious account by Alpharius himself, which he states is a lie, states that he was actually the first Primarch to be found by the Emperor. According to this tale, after his scattering Alpharius re-emerged on Terra‘s Zharinam (aka Zhari Namco) Plateau outside the proto-Imperial Palace. The young Primarch was found by the Emperor himself, who had to kill a group of scavengers present to keep the secret safe.

Thereafter, the Emperor alongside Malcador the Sigillite raised and mentored Alpharius, turning him into a being who would know the importance of the whole before the individual, secrecy, and necessity. During this time Alpharius was kept a total secret from the rest of the Imperium, even as new Primarch’s were rediscovered. One of his first major actions was disgusing himself as a First Legion Space Marine during the Palace Coup. After testing the security of the Custodes by attempting to assassinate the Emperor in a quasi-Blood Game, Alpharius became known to Constantin Valdor.

Meanwhile, Omegon emerged far from Terra on an empty nameless world. Living alone on the empty planet, Omegon was nonetheless able to come to understand that he was a manufactured being. On the abandoned world, the young Omegon discovered the Xenos weapon that would become known as the Pale Spear. When a group of Human Pirates arrived on his planet, Omegon was able to steal their ship and escape. He began a long journey towards Imperial-held systems, hearing tales of the Emperor, Primarchs, and Space Marines.

The dubious account by Alpharius goes on to state that as the Great Crusade continued, Alpharius secretly accompanied the Emperor in the rediscovery of several Primarch’s. Alpharius was present as a disguised Space Marine when the Emperor came before Lion El’Jonson and Lorgar. Inbetween these endeavors, he continued to lead the XXth Legion, the Ghost Legion, in covert operations across the Galaxy. During this time, he gathered around him a group of loyal Captains which included Armillus Dynat, Akil Gukul, Eitan, Ingo Pech, Mathias Herzog, Kel Silonius, Sheed Ranko, and Autilon Skorr. Continuing to keep both he and his Leigon’s existence hidden, Alpharius presented himself before Lion El’Jonson to offer aid during the Rangdan Xenocides and perhaps cultivate him for Warmaster over Horus. Alpharius saw the Lion as the Primarch most like him, though he continued his deceptions before the Lord of the First. During the Xenocides, Alpharius identified himself as such but denied being a Primarch.

The twins were reunited while fighting the Slaugth


During the Rangdan Xenocides Alpharius finally recieved information that he had long been waiting for, eventually coming to the world of Bar’Savor. After battling through Slaugth, Alpharius and his squad were finally able to meet Omegon, who had been battling the Xenos of the world on his own. The twins immediately recognized one another. With their “split soul” finally reunited, Alpharius and Omegon agreed the time was right to formally reveal themselves to the Imperium at large while keeping the nature of their dual existence hidden from even the Emperor, though they were not sure if he was truly unaware of it. The twin Primarch subsequently orchestrated their coming encounter with Horus, though it was Omegon who took on the title of Alpharius during the incident.



Typical of the Alpha Legion’s own nature, conflicting tales of how Alpharius was rediscovered by the Imperium exist. Many of the tales have been proven lies, while many more still remain unproven or unknown.

What is known is that Alpharius was the last of the lost sons of the Emperor to be found, some scant decades before the end of the Great Crusade. While most other Primarchs, aside from Rogal Dorn, were found on the worlds they had been cast upon, Alpharius apparently came upon Horus’ Fleet in an unnamed system.

Using a ragtag fleet of primitive one and two-man fighters he cleverly put the advance ship of the Luna Wolves‘ fleet in a precarious position, which necessitated the intervention of Horus himself. Arriving on his endangered cruiser, he soon learned that a small team of boarders was making its way towards the bridge. The cruiser was at high alert as the five boarders burst onto the bridge. Quickly four of them were dispatched by Bolt Pistol shots from Horus. The fifth one, who towered even over the Luna Wolves’ marines dodged Horus’ fifth shot, and continued to advance regardless of the gunfire. At the last instant, Alpharius stopped his assault, as both he and Horus realised the situation. Horus laughed, for he had found his last brother.

It is said that instead of immediately sending him to Terra to meet the Emperor, Horus kept Alpharius with him for some months. The two formed a strong bond, with Alpharius and his ragtag alliance quickly embracing the Imperium. Both brothers were greatly impressed with each other, although Alpharius refused to reveal his homeworld, denying that each world in the system that the brothers brought into compliance was his point of origin. Eventually, Alpharius had to journey to meet his father, the Emperor. Their meeting was, as were all times when the Emperor found one of his lost sons, surrounded with much celebration. However, since the Great Crusade was in full swing, little time was spent in idle rejoicing and Alpharius was quickly given command of the XX Legion, created just a few decades before. Renamed the Alpha Legion, they followed their Primarch on Crusade.


Alpharius quickly developed a unique approach to Astartes operations, focusing on the philosophies of initiative and flexibility, as well as extensive use of subterfuge and non-Astartes specialist operatives. This multitudinous, almost unstructured approach rankled with Roboute Guilliman, Primarch of the Ultramarines, leading him to question Alpharius’ approach to fighting. A violent discussion erupted between the two which was closed when Guilliman pointed to his own Legion’s record, something that Alpharius could never hope to achieve, since his Alpha Legion was almost two hundred years younger than the Ultramarines. They parted company acrimoniously, Alpharius believing Guilliman hated him. He resolved to ignore the Ultramarine Primarch from then on.

However, the criticism stuck; Alpharius began to push his Legion even further. More and more were the situations where he would take the more difficult course of action to force his Space Marines to grow. Plans were more complex, more subtle, while at the same time relying on more and more factors to achieve victory. Training was more intense and new strategies and approaches were constantly developed, as Alpharius sought to prove the worth of both his Legion and his martial philosophy.


Alpharius in battle-garb

The Heresy

It has long been supposed that since Alpharius was only familiar with one other Primarch, Horus, it was self-explanatory why he chose the side he did at the outset of the Heresy. Indeed, the very plan at Isstvan V where Horus struck his first blow against his fellow Legions by destroying most of the Iron Hands, Raven Guard and Salamanders Legions in a massive ambush, was very reminiscent of plans that Alpharius had created in the past. However, it is possible that there is another reason for Alpharius leading his Legion to the side of the traitors, a secret known only inside the Legion. Around two years before the beginning of the Heresy, Alpharius Omegon was apparently contacted by members of a Xenos organisation called the Cabal, who brought to him visions of the impending civil war within the Imperium, and expanded knowledge of the nature and designs of Chaos. It is believed that the Cabal convinced Alpharius that the only way to permanently defeat Chaos was to ensure that Horus was victorious. It is perhaps for this reason that Alpharius Omegon, secretly true to the Imperium and loyal to the Emperor, may have chosen to join the heretics.


Further during the Heresy, the Cabal sought to lead Alpharius’s and Omegon’s actions in order to make Horus victory easier. One such action was the ordeal against the Raven Guard with the intent of preventing Corax from rebuilding his legion after the blow struck on Isstvan V. Some Alpha Legion marines were infiltrated, under the direction of Omegon, in the Raven Guard thanks to Alpha Legion apothecaries grafting the facial traits of some dead Raven Guards over the face of their own legionaries. Once known, through their infiltrators, that the original genome of the Primarchs was in the hands of Corax, Omegon acted in order to recover the secret knowledge so the Alpha Legion could be expanded in future times. With the help of renegade Mechanicum magos Unithrax, the Alpha Legion tainted the original genome recovered from the laboratories of The Emperor on Terra. This was accomplished introducing a virus-vectored mutagen based on daemonic blood making the successive Raven Guard implantation’s result in operational but deeply-mutated Astartes exhibiting scales, horns, fangs, tails, overgrown muscles and similar features.

Fabius was duped by Alpharius who gave him a tainted Astartes genome.

Meanwhile, Omegon bound to his service, although not directly consistent of the fact, both a renegade Mechanicus faction and some representatives of the ancient and noble guilds of Kiavahr. He pushed them to open rebellion against the Raven Guard and, in the chaos resulting from the battle, he personally recovered all data stored in Corax laboratories as well as the tainted original genome. In the aftermath, Alpharius was obliged to give the obtained data to Horus who handed them to Fabius Bile for deeper research. What Bile did not know, was that the data were practically useless since incomplete at best. Of course, the Alpha Legion kept for itself the integral data as well as the corrupted genome. The Plan of Alpharius had always been to use the Data to raise the Alpha Legion over all other legions, loyalists and traitors. After this action, Omegon left the Cabal representative Athithirtir on board his ship into the void stating that the legion would fulfill its engagement on its own, without external interference or control.


Alpharius (or Omegon) battle Rogal Dorn during the Heresy.

Death & Rebirth

In preparation to infiltrate the Sol System in the Solar War, Alpharius used his Librarians to seemingly switch bodies with his trusted Harrowmaster Kel Silonius. To ensure secrecy, Alpharius also erased his own memories and took on Silonius’ persona. As the real Silonius led a a fleet of 200 Alpha Legion warships into the Sol System, Alpharius led a Headhunter and human operative team in setting the stage for its arrival through acts of sabotage and preparation. During the final action, Alpharius’ memories were restored by psychic trigger.

During the subsequent Battle of Pluto Alpharius confronted Rogal Dorn in a chamber locked inside of the Hydra Fortress Moon in Pluto‘s orbit. He killed Archamus‘s team hunting him but left Archamus mortally wounded and alive to watch as Dorn teleported into the chamber. Both Dorn’s Huscarls and Alpharius’s Lernaeans teleported in, and the primarchs slaughtered the other’s warriors. The two battled, with Alpharius dealing Dorn many wounds, using his speed to stay out of reach. Throughout the fight, he tried to convince Dorn that he was there to teach him how to win, to expose his weaknesses, that he could not win the current war, and how there needed to be a new type of war. He also claimed that Dorn didn’t understand what he was fighting for, and they both cared about the future. Only he knew the truth regarding the conflict, and he did not fight for Horus but for Dorn.

Eventually, he tried to kill Dorn with a blow from his Sarrisanata (“Pale Spear”), Archamus saw the strike and tries to intervene but reels harmlessly off of the spears haft. Alchamus was unaware that Dorn had seen the strike, the Imperial Fists Primarch outplaying Alpharius by using a move he’d used against a giant Ork decades earlier, Dorn stepping into the shot and tanking it in his shoulder to pin Alpharius in place, he then grabbed the spear and sliced Alpharius’s hands from his wrists before he slashed Alpharius across the chest, stabbed him with his own spear, and finished by cutting through Alpharius’s skull with his mighty chainsword, Storm’s Teeth.

Dorn then hid from the loyalists Alpharius’s appearance within the system and his death, promoting others with direct knowledge of the events to Huscarl to replace those who died. Dorn sought to deny Alpharius any acknowledgment or honor. Far away, Omegon sensed the death of his twin and he grew distant. Upon being notified that Horus demanded to speak with Alpharius, Omegon took up the name and became his twin brother.

Alpharius (or at least an Alpha Legionnaire claiming to be him) reappeared alone on Ullanor during the muster of traitor forces there in preparation for the Siege of Terra. No other Alpha Legion forces were present in system, making many other traitors wonder how Alpharius could even be there at all. Before Horus’ Dark Triumph on Ullanor, Alpharius appeared in the Warmaster’s command tent and gave him a cylinder which contained a detailed layout of all of the Sol System‘s defenses and infrastructure. Alpharius then took out a dagger and shattered it in his hand, throwing the pieces at Horus’ feet before leaving. Abaddon demanded that Horus kill him for such insolence, but the Warmaster instead let Alpharius go.


During the Heresy, Alpharius (or after his apparent death on Pluto, Omegon) appeared more interested in proving his own Legion’s worth by fighting, at every chance he got, the best of the Loyalist legions. Thus, even after Horus was cast down and the Heresy over, the Alpha Legion kept on fighting, moving more and more towards the galactic east, towards the Ultramarines. It was on the world known as Eskrador that Alpharius-Omegon and Roboute Guilliman would meet for the last time.

Believing that Guilliman would adopt his standard Codex deployment procedures, Alpharius-Omegon was surprised by the Ultramarines, as a splinter force including their Primarch made a quick strike at the Alpha Legion’s headquarters. Both Primarchs met in combat and Alpharius-Omegon was killed. Believing the combat over, for who could ever survive the loss of their Primarch in battle, the Ultramarines were taken by surprise by the remaining elements of the Alpha Legion, when they struck back a day later. After a week of constant fighting and heavy losses, the Ultramarines strike force managed to reunite with their main elements, and quickly evacuated the planet.

Even though they had lost their Primarch, the Alpha Legion had soundly beaten the Ultramarines, who proceeded to bombard their foes’ position from outer space. It should be noted, however, that Alpharius’s death is still considered suspect even by the Ultramarines, and he may still be at large. Alpharius’ apparent earlier death during the Battle of Pluto during the Heresy complicates the mystery further, as it may have been Omegon who really died on Eskrador, if at all. Many within the Alpha Legion, such as Quetzel Carthach seem to believe that it was Omegon who was slain on Eskrador, though others like Occam believe him to still be alive. Whatever the truth, the Primarch of the Alpha Legion has not been seen since.


At some point after the Heresy, word reached the High Lords of a Chaos Lord claiming to be Alpharius ravaging the moons of the Danevra Sub-sector. Debate raged about whether this could potentially be the case, for the Primarch’s death has been recorded more than once across the span of Imperial history. Nonetheless, the Grand Master of Assassins dispatched a force of six Vindicare Assassins. Over a number of years they identified and slew a dozen Alpha Legion champions bearing the name of Alpharius, but the reports of raids upon the sub-sector’s mining operations only intensified. Five years later, the heads of all six Vindicare Assassins were found frozen in the food storage halls of the High Lords.

A partly redacted quote credited to Alpharius Omegon also exists, dated to around the year 123 (though the millenium is redacted). It likens the Chapter to an unpredictable serpent, and says that they have retained their identity and purpose while other Space Marines have all fallen to stagnation and damnation. It goes on to say that they are uncertain allies to the Chaos Gods, are unaffected by the lies of the xenos, and are a necessary evil to the Imperium, acting as both its poison and antidote, in an unavoidable destiny that they have created for themselves and others.

Learn More of the Alpha Legion

So do you think the Alpha Legion are really traitors, or are they pulling off a 10,000 year “inside job” on Chaos?

Author: Larry Vela
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