Alpha Legion was the XX Legion of the Legiones Astartes, led by Alpharius and Omegon – a pair of primarchs whose identities are shrouded in mystery. Their motto “We are Alpharius” captures their philosophy: disinformation, infiltration, and psychological warfare.

Unlike other legions, the Alpha Legion did not operate from a single homeworld but from secret bases across the galaxy. During the Horus Heresy, they sided with the traitors, but their true motives remain unclear – perhaps they sought to save humanity through the destruction of the Imperium.

In the Horus Heresy system, Alpha Legion has rules such as Lies and Obfuscation, making their units count as 2″ further for shooting, charging, and reactions. This allows them to dodge fire and complicate enemy maneuvers. Their forces include Headhunters, Lernaean Terminators, Saboteurs, and heroes like Exodus, Armillus Dynat, and Alpharius himself.