Arkos was once a loyal Space Marine Captain, a proud officer of the Alpha Legion during the Great Crusade, but during the Horus Heresy, he, along with the rest of the XXth Legion followed the Arch-Traitor Horus into damnation. As would later be discovered Arkos became one of the most trusted elements of the Primarch Omegon, twin to Primarch Alpharius, and acted as his equerry while the Alpha Legion conducted its own campaign against the Emperor of Mankind’s Loyalist forces. After Horus' defeat at the hands of the Emperor at the Battle of Terra, he fled alongside the remains of his Legion to the Eye of Terror and continued the Alpha Legion’s Long War against the False Emperor at every opportunity that has presented itself ever since. He lead a powerful warband of Alpha Legion Space Marines