Alpharius Omegon (also known as the Last Primarch) was actually a pair of identical twin brothers, and one of the twenty Primarchs created by the Emperor of Mankind in the earliest days of the Imperium of Man, just after the end of the Age of Strife in the 30th Millennium. Like the other Primarchs, Alpharius and his twin brother Omegon were transported from the Emperor's gene-lab beneath the Himalayan Mountains of Terra through the Warp by the Chaos Gods and placed on a far-away world in an attempt to prevent the coming of the Age of the Imperium and the expansion of the ordered Imperium of Man across the Milky Way Galaxy. Alpharius Omegon was eventually rediscovered by the Primarch Horus and sent to meet his father the Emperor on Terra, who placed him (and secretly, his brother) in command of the XX Space Marine Legion, the Alpha Legion, during the Great Crusade of the 31st Millennium.
Secrets and Lies
It should be noted that the Alpha Legion's trademark secrecy extends to the records of their Primarch. Little recorded information on his background and homeworld 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 Last 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 of the Alpha Legion's Primarch is apparently told to no one outside the Legion, and has always been thus. For, unlike any of the other Primarchs, Alpharius actually has an identical twin: Omegon. It is unknown if the Emperor intended this when he created the last Primarch, or was ever even aware that his final Primarch's embryo had split into two identical fetuses during their gestation before they were stolen away by the Ruinous Powers. Alpharius and Omegon are both the Primarch of the Alpha Legion, although "Alpharius" was the public face of the Legion and appeared as the more senior of the two. Though as both Primarchs were physically identical it is possible for them to switch places and have "Omegon" play the public role of the Legion's Primarch. They have been described as "one soul in two bodies" and collectively have been referred to as simply "Alpharius Omegon". While the Astartes of the Alpha Legion made attempts to all look alike, both Alpharius and Omegon were still somewhat distinctive. Taller than the rest of the Legion, slightly copper-skinned, bald and possessed of a heavy brow, they somewhat resembled their brother Primarch, Horus. Unlike him, Alpharius and Omegon had piercing eyes that seemed to glitter, appearing to shift colour from a cold arctic blue to a shimmering green. The overall impression given by Alpharius Omegon was one of nobility and intelligence. One way to tell the two twin Primarchs apart was when Omegon was performing as commander of Effrit Stealth Squad; large portions of his Power Armour and other gear were painted black and otherwise darkened. The armour worn by Alpharius was not particularly different from that of an ordinary Alpha Legionary.
The Great Crusade
Alpharius was the last of the lost Primarch sons of the Emperor to be found, only a few decades before the end of the Great Crusade and the start of the Horus Heresy. While most of the other Primarchs, aside from Rogal Dorn, were found on the worlds they had been cast upon by the Ruinous Powers of the Warp, Alpharius Omegon apparently came upon Horus' fleet himself in an unnamed star 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 boarder, who towered over the Luna Wolves' Space 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.
Pleased beyond measure, instead of immediately sending him to Terra to meet the Emperor of Mankind, Horus kept Alpharius with him for some months. The two formed a strong bond, with Alpharius and his ragtag alliance of pirates 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 star system that the brothers brought into Imperial Compliance was his point of origin. Eventually, Alpharius had to journey to Terra 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 Space Marine Legion, created from Alpharius' genetic material just a few decades before. Renamed the Alpha Legion, they followed their Primarch on the Great Crusade.
Alpharius quickly developed a unique approach to Adeptus 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, greatly rankled Roboute Guilliman, the Primarch of the Ultramarines, leading him to question Alpharius' approach to war. 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 Ultramarines' Primarch from then on.
However, the criticism stuck; Alpharius began to push his Legion even further to display the superiority of his chosen way of war. More and more Alpharius pushed his Legion into situations that would require the more difficult course of action to force his Space Marines to grow as warriors. Plans were made 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 to the Imperium at large.
The Horus 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 Horus Heresy. Indeed, the very plan at Isstvan V where Horus struck his first blow against the Loyalist Space Marine 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. Approximately two years before the beginning of the Heresy, Alpharius Omegon was apparently contacted by members of a xenos organisation led by the Eldar but comprising an alliance of individuals drawn from a host of different intelligent species, 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 the Ruinous Powers of Chaos. It is believed that the Cabal convinced Alpharius Omegon that the only way to permanently defeat Chaos in the galaxy was to ensure that Horus was victorious in his rebellion against the Emperor. 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 Traitors who swore their souls to Chaos.
The Cabal, through its only known human agent John Grammaticus, explained that the Cabal had foreseen two possible outcomes to the coming Heresy. The first vision had the Alpha Legion remaining loyal to the Emperor and fighting against Horus, ending in the Emperor's victory. However, the Emperor would be gravely wounded and entombed inside the cybernetic sarcophagus of the Golden Throne, neither alive nor dead and no longer able to actively guide humanity. Ten millennia would pass and the Imperium of Man would be fated to slowly decay, until ultimately Chaos would return resurgent and defeat mankind, condemning humanity to eventual extinction. The second outcome had the Alpha Legion joining forces with Horus and Chaos Undivided and fighting the Emperor. In this vision, Horus was victorious and slew the Emperor. The Traitor Legions would defeat the Loyalists and Terra would belong to Horus, now the greatest Daemon Prince of Chaos. The vision continued with Horus, after slaying his father, shocked into sanity by his conscience and violently freed from Chaos' corrupt hold over him. Disgusted with himself and loathing what he had done, Horus would seek to exterminate the Chaos-corrupted human race in a vast orgy of bloodshed which would consume the entire Imperium in a single century. Though humanity would become extinct, the Chaos Powers would also be destroyed by the destruction of mankind, since ultimately their existence largely depended upon the collective psychic emanations of humanity in the Warp.
The Cabal, an alliance of xenos Eldar and a somewhat unwilling human psyker named John Grammaticus, burdened the Alpha Legion with these two visions which they promised would come to pass. The Alpha Legion were told the fate of the entire galaxy rested upon their Legion's decision alone. The Cabal had no time to reach or to attempt to convince another of the Space Marine Legions of what was to come. Either the Alpha Legion ensured the human race died in a century of incredible violence, sparing the other races of the galaxy, present and future, from Chaos forever, or they ensured the human race and the Imperium lived on for ten thousand years of bloodshed and decay, dooming the entire galaxy to brutal war and the eventual triumph of Chaos.
The Alpha Legion decided to join Horus' rebellion and made the decision that they believed the Emperor would have chosen, to sacrifice humanity for the ultimate eradication of Chaos from the universe. Yet their sacrifice seems to have been made in vain, as Horus did not find victory and the Imperium persevered despite the Alpha Legion's decision to support Chaos. This can only lead one to wonder if the Cabal and their future predictions were wrong, if the Cabal secretly served the interests of Chaos and lied to Alpharius simply to corrupt yet another Astartes Legion or if something else occurred that has yet to be discovered. It is noteworthy to mention that John Grammaticus, the human agent who made first contact with the Alpha Legion on the Cabal's behalf, was a man very similar to the Emperor himself. John was a powerful mutant psyker who had been alive for thousands of years, and had even met the Emperor face to face once, before the Emperor had finished uniting the various factions of men on Terra during the Unification Wars of the 30th Millennium.
During the Horus Heresy, Alpharius Omegon appeared more interested in proving his own Legion's worth by fighting, at every chance he got, the best of the Loyalist Legions. In the aftermath of the Horus Heresy, the Alpha Legion did not retreat to the Eye of Terror like the other Traitor Legions; instead they moved on into the galactic East, following new objectives of their own devising. Whether or not being brought to battle with the Ultramarines was one of these objectives is unknown, but it occurred all the same. It was on the world known as Eskrador that Alpharius and Roboute Guilliman would meet for the last time. Believing that Guilliman would adopt his standard deployment procedures as later outlined in the Codex Astartes, Alpharius was surprised by the Ultramarines, as a splinter force including their Primarch made a quick strike at the Alpha Legion's headquarters. Alpharius was reportedly happy with such a development, as it allowed him to demonstrate the superiority of his flexible, multitudinous and unexpected military strategies over the notoriously precise, methodical and perhaps even tactically moribund Ultramarines. Both Primarchs met in combat and Alpharius was killed. Believing the combat over, for what Astartes Legion 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. The Ultramarines who had launched the attack on the Traitor Legion's headquarters were harried so mercilessly that by the time they had returned to the main body of the Ultramarine force their casualties were almost total. 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 orbit. It should be noted, however, that Alpharius' death is still considered suspect even by the Ultramarines, and he may still be at large. On the other hand, it is possible that "Alpharius" did indeed die and his twin "Omegon" took sole command of the Alpha Legion.
Unlike the other Traitor Legions, most of the Alpha Legion does not reside in the Warp, but rather roams the galaxy in warbands of warriors, each of which is trained to act independently of each other in pursuit of their greater cause. In this way the Alpha Legion was by and large the only Traitor Legion not to succumb to the mutations of Chaos, an outcome that may also have been dictated by their continued secret loyalty to the Emperor of Mankind.
Following the Battle of Eskrador, the Alpha Legion fractured in order to hide from the Imperium. Small, autonomous warbands were left in Imperial space where they set up secret bases in asteroid fields, Space Hulks and barren, unpopulated worlds. These units launched frequent attacks against military targets that were weakened by the Heresy and even today still pose a threat to Imperial starships, settlements and garrisons. The Alpha Legion's warbands further spread and coordinate Chaos Cults throughout the galaxy in order to instigate massive planetary revolts against Imperial rule. These insurrections are often used to lure Imperial forces away from worlds the Alpha Legion wants to attack, paving the way for large-scale assaults of Chaos Space Marines from the Eye of Terror.
The Alpha Legion's role in spreading heretical Chaos Cults across the Imperium has earned them the loathing of the Inquisition, whose Ordo Malleus and Ordo Hereticus have devoted considerable resources in finding and destroying their secret bases. The Alpha Legion has been declared wiped out by the High Lords of Terra no less than three times, in the 31st Millennium, the 32nd Millennium and the 39th Millennium. These claims have always been disproved by the continued assaults of the Legion. The Alpha Legion has suffered heavy casualties on many occasions since the end of the Heresy, yet its continued large numbers has led many Imperial observers to conclude that they are recruiting new members into the Legion and thus have managed to maintain a supply of untainted gene-seed, also a rarity for Chaos Space Marines.