Revuel Arvida - Janus: With his body ravaged by the Flesh-Change, Arvida clung to life by the merest thread. Placed in a stasis sarcophagus, he was taken to the deepest subterranean levels of the Imperial Dungeon, located far below the Imperial Palace. There Malcador attempted to bind a fragment of Magnus the Red's psyche -- one of the many shards of the Crimson King's psychic soul which remained on Terra after he had foolishly utilised a sorcerous spell to break through the psychic shielding of the Imperial extension of the Webway to warn the Emperor of Horus' perfidy.When Magnus breached the Emperor's psychic wards over the Imperial Palace on Terra, his soul was broken -- shattered like a mirror thrown in anger. Effectively his soul had fractured into a vast multitude of different aspects, each representing a part of the primarch's personality.All that remained on Terra was the aspect of Magnus that had represented the ever-loyal son of the Emperor. It was this shard of Magnus' soul which Malcador hoped to utilise while Arvida's body was in the last stages of the Flesh-Change.The Sigillite hoped to resurrect a form of Magnus so that he could take his place upon the Golden Throne and fulfill the destiny the Emperor had originally intended for His psychically-potent son -- to connect the myriad worlds of the Imperium with a Human version of the Aeldari Webway.Worried at what was being done to Arvida, Jaghatai Khan rushed to his aid and ordered the Sigillite to stop what he was doing -- but it was already too late. As the shard of Magnus was too powerful to contain, Arvida's severely mutated body began to be consumed by psychic fire.Malcador intended to euthanise the sorcerer, but the Khagan insisted that Arvida was his ward and must be given a chance to succeed or fail on his own, without any outside interference. The primarch then proceeded to destroy the arcane machinery in the chamber, freeing the amalgam of Magnus/Arvida from the suppression fields and psychic wards.The psychic energy that consumed Arvida's body soon coalesced and solidified into solid matter, taking the form of an Astartes, but without any sign of the Flesh-Change. One of the being's eyes was swollen with scar tissue, much like the Crimson King's own missing eye. This entity was not the shadow-primarch trapped in a host body like Malcador had intended, nor was he entirely the Legionary formerly known as Revuel Arvida, for he had become much more.When referring to himself, he asked to be called "Ianius." Ianius apologised for not becoming Magnus due to the fact that they both were going to end up dying in the near-future.The name Ianius would later be transcribed as "Janus," one of the eight Space Marines chosen by Malcador the Sigillite and approved by the Emperor to lay the foundation of what was to become the Inquisition and the Grey Knights Chapter of the Space Marines.Years later, following their personal audience with the Master of Mankind in the final days of the Horus Heresy, Malcador took the eight Space Marines to the moon of Saturn called Titan, and oversaw the initial creation of the Grey Knights as a fully-functioning Chapter. But the Sigillite could not remain to oversee their evolution, so he selected one of the eight to lead the Chapter in the years to come.Malcador's final act before returning to Terra for the climax of the Heresy was to appoint Janus as the first Supreme Grand Master of the Grey Knights, to guide the nascent Chapter through its first challenges.Legends of the Grey Knights' founding lord are as numerous as there are stars in the night sky -- the Chaos champions he slew, the wars he won, the Daemons he banished -- and none alive now know how much they have been twisted through the centuries.