Ahriman - Great Crusade: Eventually the fleets of the Great Crusade reached the world of Prospero, and the rediscovery of the Primarch Magnus the Red, the Thousand Sons' genetic progenitor, could not have come soon enough. The discovery of their genetic sire marked a turning point in the fortunes of the Thousand Sons Legion, for Magnus possessed a means to seemingly cure the extreme mutational effects of his genetic material in his gene-sons and the devastation they had wrought upon his Legion.However, Magnus had sacrificed much in order to attain this victory, including the loss of his eye in the effort, which involved secret bargains with the Ruinous Powers of the Warp to gain the knowledge required to halt the mutations.Little is known about Ahriman's exploits during the Great Crusade. Additionally, Ahriman was seconded by the Thousand Sons for 5 Terran years to the Word Bearers Legion, which he found to be an uncomfortable experience because of the Word Bearers' insistence on worshipping the Emperor of Mankind as a divine being in violation of the tenets of the Imperial Truth.Despite this, Ahriman still managed to strike up a friendship with the Word Bearers' Chaplain Erebus. Ahriman is also one of the few Astartes from this period who was publicly supportive of the Emperor's initiative to require civilian Remembrancers to record the exploits of the Legiones Astartes and the other Imperial military forces during the Great Crusade, as he hoped that an accurate record of the Thousand Sons' exploits would teach the wider Imperium to no longer be afraid of or prejudiced against psykers or the use of psychic powers.The earliest surviving mention of an Ahzek Ahriman in Imperial records occurred during the Aghrou Campaign in the final years of the Great Crusade's second century, a standard action of that time in which a pre-industrial Human world was brought into Imperial Compliance by the 28th Expeditionary Fleet, with aid from a contingent of the Space Wolves Legion.Ahriman risked his Primarch Magnus the Red's wrath when he led a search team in pursuit of the primarch after Magnus had made himself absent from his Legion, despite Magnus' prior insistence that he was not to be disturbed under any circumstances. This incident represented the first time that Ahriman was known to have mistrusted the judgement of his primarch and then acted contrary to his expressed desires. It would not be the last.Towards the end of the Aghrou Campaign, when a contingent of Space Wolves Astartes arrived to convey a message to Magnus from their own Primarch Leman Russ, Ahriman found fellowship with the Space Wolf Rune Priest Othere Wyrdmake, during which he shared information on the Thousand Sons' psychic disciplines in what he thought was a meeting of convivial brother Astartes, but which later proved treacherous when the Space Wolves used this conversation against the Thousand Sons' position in favour of supporting continued use of the psychic arts at the Council of Nikaea.Ahriman's relationship with the Rune Priest proved useful when both the Space Wolves and the Thousand Sons were forced to engage in combat with alien "weaponforms" similar to Imperial Titans and the Daemons of the Warp before leaving Aghoru. This represented the first time that both Legions had come into contact with the realities of Chaos.It was also at this time that Ahriman was charged by his primarch with inducting the Remembrancer Lemuel Gaumon into the ways of the Thousand Sons. This was intended to develop Gaumon's own psychic abilities and thus through him spread Magnus' pro-psyker beliefs throughout the Imperium. Ahriman took Gaumon on as his Probationer, and spent a significant amount of time training the Remembrancer and teaching him the sorcerous knowledge of the Thousand Sons during the time leading up to the Fall of Prospero.This training included allowing Gaumon to accompany the Thousand Sons on combat missions during the pacification of the world of Heliosa, where Ahriman was present for the sudden resurgence of the mutational flesh-change within the Legion and the granting of the Emperor's peace to the afflicted mutant Thousand Sons Astartes by the Space Wolves' primarch, Leman Russ. The return of rampant mutation to the Thousand Sons after Magnus had previously promised that he had banished its danger forever deeply hurt Ahriman, to the point that his feelings of betrayal were detectable even to a mortal like Gaumon.Ahzek Ahriman was present at the great review of the Imperial military on the world of Ullanor at the conclusion of the Ullanor Crusade when the Emperor named Horus as the Warmaster of the Great Crusade. More importantly, Ahriman attended the great Imperial conclave known as the Council of Nikaea when the Emperor outlawed the use of psychic abilities within the Space Marine Legions and sorcery across the Imperium.To Ahriman the Council of Nikaea felt instead more like a trial of the Thousand Sons. He felt betrayed once more by the Emperor's decision. Far worse was the fact that the first person to step forth and accuse the Thousand Sons of engaging in the malignant and dangerous practice of sorcery was the fellow Astartes he had believed to be his friend within the Space Wolves Legion, the Rune Priest Othere Wyrdmake.Betrayal seemed to hammer Ahriman from every side as it was also at this time that he first learned that Magnus had not only been aware of the Ruinous Powers' existence within the Immaterium, but that he had likely struck some form of malign bargain with them which had resulted in the end of the rampant mutations within the Thousand Sons Legion.Aghast at a revelation which gave some truth to the charges of heresy by the the Space Wolves and the Emperor's fears of allowing the practice of sorcery, Ahriman found his trust in his primarch further eroded, though Magnus ultimately used his own potent psychic abilities to remove the details of the deal he had struck with the Dark Gods from his Chief Librarian's mind before Ahriman could understand its full import.