Garviel Loken - Istvaan III Atrocity: This attitude cost Loken the trust of not only his two Mournival brethren but also of Horus himself, who emerged from his healing at the hands of the Chaos Cultists of the Serpent Lodge a changed man, one riven by jealousy, egotism, hatred for his father the Emperor and the lust for absolute power. He was a man who had given his soul to the Chaos Gods in return for the powers of the Warp.Now falling firmly into the grip of Chaos, Horus chose the world of Isstvan III to dispose of those members of the four openly declared Traitor Legions -- the Sons of Horus, the Emperor's Children, the World Eaters and the Death Guard -- that he could not trust to follow him or serve the Chaos Gods in his new quest to dethrone the Emperor and rule the galaxy himself.Loken and Torgaddon, as well as approximately one-third of the 4 Legions' Astartes who were judged to be Loyalists, were sent to the capital city of the planet of Isstvan III under the pretext of putting down a rebellion against the Imperium of Man by the Slaaneshi-corrupted Planetary Governor Vardus Praal only to be slaughtered by Life Eater Virus Bombs launched from the Warmaster's orbiting fleet.A last minute warning about the imminent betrayal from their friend Captain Saul Tarvitz of the Emperor's Children provided some of the Loyalists, including Loken and Torgaddon, with enough time to seek shelter and thus survive the resulting virus plague and the firestorm that followed that killed all of Isstvan III's 8 billion people.Even with Tarvitz's warning, at least a third of the Astartes Loyalists did not make it to shelter before the bombs dropped, or emerged from the shelter too early, believing the attack to be over, only to be obliterated in the subsequent firestorm that ignited all the noxious, decaying gases released by the virus victims' bodies.With Horus' betrayal now in the open, Loken and Torgaddon and the other surviving Loyalists of their Legion took up the name Luna Wolves once again to symbolise their split with the Sons of Horus as they openly fought against the Warmaster's Traitor Legions.They fought using a defensive strategy intended to bleed the Traitor Legions for several solar months to allow news of Horus' betrayal to reach the Emperor. They managed to hold out on Isstvan III for almost 2 months before the final battle, in which Horus Aximand and Abaddon traveled to the surface to confront Loken and Tarik face-to-face. Loken fought bravely against Abaddon but he was critically wounded, and lay helpless in the final orbital bombardment of the planet by the Warmaster Horus' fleet, which brought the resistance of the Loyalists to its end.However, by some twist of fate, or through the will of the Emperor, Loken did not die in the bombardment. Solar months later, well after Horus' fleet had moved on to face the Emperor's Loyalists at the Drop Site Massacre on Isstvan V -- where 4 more Astartes Legions declared their open allegiance to Chaos and to Horus -- Loken finally managed to dig himself out of the rubble of the Choral City.Unfortunately, Loken's mind had been broken by the trauma of the betrayal and his wounds and he had lost both his memory and his identity. Instead, he took up a new role and named himself "Cerberus" after the ancient Terran legend of the hound who guarded the gates of the Underworld. Loken chose this identity because he believed that death had rejected him.He became the "monster" who now haunted the burnt and broken ruins of Isstvan III for over a Terran year, killing the other supposed "survivors" of the betrayal, believing himself to be the last Loyalist Space Marine in existence.