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Warhammer 40k’s Alpharius Omegon - the Alpha Legion Primarch

All the secrets, lore, and tabletop rules of Warhammer 40k's Alpharius Omegon, Primarch of the Alpha Legion and galactic man of mystery.

Warhammer 40k Alpharius Omegon guide - Warhammer Community artwork showing Alpharius in full plate with a spear

Of all Games Workshop’s grimdark sci-fi characters, Warhammer 40k’s Alpharius Omegon is perhaps the most steeped in secrets and lies. His Space Marine gene-sons, the XX Legion Astartes – Alpha Legion – were masters of subterfuge, counterintelligence, ambush, sabotage, infiltration, and deception.


Though equally capable of fielding the massed infantry and armour formations of the other Legions, the purple-armoured Space Marines of Alpharius preferred to fight undetected, even hiding their presence from Warhammer 40k factions who were supposedly their allies in the Imperium of Man.

During the Great Crusade, Alpha Legion campaigns used huge networks of operatives, turncoats and spies to gather information and spread disorder through enemy forces. Whole worlds were brought to compliance with hardly a shot fired, their armed forces picked apart by audacious, intricately planned schemes.

Most enigmatic of all the Warhammer 40k primarchs, Alpharius had no compunction about spending the lives of his legionnaires to further his agenda – and yet it’s said Alpharius had a particularly close bond with his sons. Reputedly close to the size of a normal astartes (compared to his hulking brothers), Alpharius often swapped places with his bodyguard marines during official events, so similar were their appearances. Ask an Alpha Legionnaire his name and you would be answered: “I am Alpharius.” This was just one of the many secrets held by the legion that Alpharius never shared with his brother primarchs.

This guide explores what little is known of the most elusive Primarch, his motivations for joining the traitor Warmaster Horus Lupercal, and scratches the surface of his untold secrets.

Warhammer 40k Alpharius Omegon guide - author photo showing Alpharius and Lernean Terminator models on the tabletop

Heads of the Hydra

Alpharius was the last of the Primarchs to be discovered and reunited with his legion. Beyond that, nothing certain can be said. This is by design: the Alpha Legion are masters of deception.

One theory holds that the Luna Wolves discovered Alpharius late in the Great Crusade. A Luna Wolves battleship had been laid low by the cunning actions of a fleet of far smaller, inferior human vessels. Enraged, Horus personally led a reprisal fleet, but this became mired in feints, ambushes and traps.

Finally the Vengeful Spirit entered the fray, dashing aside all resistance, but a single assassin was able to board Horus’ flagship and murder his way to the throne room. When Horus and this impossible warrior finally met, Horus’ recognised at once that this was his last, lost brother.

Even if this story is true, it is not the whole truth. There was a secret Alpharius kept from all his brother Primarchs. Alpharius had a twin brother, Omegon.

Warhammer 40k Alpharius Omegon guide - Warhammer Community artwork showing a huge army of Alpha Legion space marines during the Horus Heresy

For the Emperor!

Most attribute Alpharius’ fall to the ruinous powers to his personal connection to Horus. Yet his and Omegon’s motivations are far more subtle. While covertly supporting the Imperial Army’s compliance of the planet Nurth, the Alpha Legion were contacted by operatives of the ancient and mysterious Cabal. The Cabal were an inter-species alliance of ancient xenos dedicated to combating a force they called the Primordial Annihilator, the forces of Chaos.

The Cabal gave the twin primarchs visions of the forthcoming civil war. If Horus triumphed, the last shard of his nobility would drive him to ever more destructive acts, an unending war that would drive the human species to extinction.

Yet for this terrible cost, the forces of Chaos also would be undone. If the Emperor won, he would only do so at the expense of his own mortality. He would become a psychic horror lashed to the Golden Throne, and his Imperium would fall into a spiral of stagnant misery that would see the forces of Chaos grow in power until they entirely consumed the galaxy.

Thus, the Alpha Legion sided with the Warmaster in the Horus Heresy, but retained their battle-cry: “For the Emperor!” There is method in their madness… and madness in their method.

Warhammer 40k Alpharius Omegon guide - author photo showing a force of Alpha Legion miniatures on the table

I am Alpharius… perhaps

The Legion’s actions during the Heresy seemed to help and hinder traitors and loyalists with equal measure. Yet the Alpha Legion was the first to assault the Sol system. They had planned for it for decades, before they ever decided to side with Horus.

In a series of double-bluffs so deadly secret he even hid it from himself, Alpharius employed psykers to wipe his own mind so he could infiltrate into the Imperial palace without detection.

Alpharius made a brazen declaration of intent against the Imperial Fists primarch Rogal Dorn, destroying all the great statues of the Primarchs in the Imperial Investiary, save for his own and that of Dorn.

This attack was so brazen that Dorn declared it must be a feint intended to pin him into the sector, leading the main strength of the Imperial fleet to reinforce the surrounding sectors.

Warhammer 40k Alpharius Omegon guide - Warhammer Community artwork showing Alpharius battling Rogal Dorn

Alpharius’ scheme was wildly more ambitious. A fleet of Alpha Legionnaires had been travelling, unpowered and undetected, into the Sol system for years. They brought their vessels to combat readiness just as traitor cells were activated throughout the system in bloody insurrection.

The Legion’s target was the astropathic relay on Pluto’s moon of Hydra. Alpharius rendezvoused with his Legion there. If Hydra fell, Alpharius would claim Pluto and the fortress moons orbiting it without anyone on Terra knowing what had occurred.

Yet Alpharius had underestimated his stolid brother. Dorn had seen through Alpharius’ bluff, and his fleet raced to intercept the Alpha Legion. The two primarchs met in mortal combat, and all the guile of the hydra could not save Alpharius from his gold-clad brother’s terrible wrath.

The Alpha Legion was shattered, their Primarch Alpharius dead. Yet it was also a victory. Every detail of Dorn’s defensive stratagems were revealed to the Legion. On the plains of Ullanor, the surviving twin Omegon (as far as we know?) silently presented the Warmaster with the data he had bought with his legion’s blood.

Warhammer 40k Alpharius Omegon guide - author photo showing the Forge World model of Alpharius

Alpharius model – Horus Heresy

In games of Warhammer: The Horus Heresy, an army led by Alpharius’ model can seize the initiative on roll of a 4+, starting the mind-games while your opponent is still deploying.

Unlike the other Primarchs, Alpharius had the rare ability to conceal himself as an ordinary (if somewhat large) legionary, and, appropriately enough, on the tabletop, you can secretly select a unit of Alpha Legion infantry that he is hiding inside.

You don’t even need to put Alpharius’ model on the table until he pops out: you’re playing a deadly shell game against a foe who must guess which tactical squad is hiding a deadly Primarch.

Warhammer 40k Alpharius Omegon guide - Forge World sales photo showing the models for Alpharius and the Lernean Terminators

Though the Alpha Legion pride themselves on uniformity of purpose and flexibility of command, Alpharius exerts incredible sway over his sons.

When he is on the table, all Alpha Legionaries gain the Preferred Enemy (everything) special rule, letting them reroll hit and wound rolls of 1, and the Primarch himself can use his Cognis Signum to grant a friendly unit +1BS, instead of shooting his own Plasma Blaster.

Though not as physically daunting as his brothers, Alpharius has a respectable five WS7 attacks with the Pale Spear, an AP1, Armourbane, Instant-Death weapon that strikes at Initiative 6.

With the new edition of Warhammer: The Horus Heresy out now, we can’t be sure if Alpharius’ new rules will change the game substantially, but he will remain an insidious mastermind who unravels your opponents plans, and catches them in his own devious machinations.

Hydra Dominatus!

For more exploration of Warhammer 40,000’s prehistory, check out our guides on all the Space Marine legions, and the best Horus Heresy book order to read the novels in.

With thanks to Paul for photos of his gorgeous Alpha Legion army.