Ahriman - Exile: Ahriman had been exiled from Sortiarius, but so too was his cabal of sorcerers. Yet in their absence, it was Amon who became determined to find all the secrets of the Rubric and perhaps restore some of his mindless, undead brothers back to life. Over the next one thousand standard years as he continued to amass more power, Amon founded his own powerful warband of Heretic Astartes known as the Brotherhood of Dust which consisted of many exiled Thousand Sons.It was Amon who also gathered voidships, other Chaos Space Marines, hundreds of Rubricae and a number of apprentices, who themselves soon became formidable Chaos Sorcerers in their own right. It was Amon's intent to see the suffering of his Legion ended, for he would undo the fell magic of the Rubric that had doomed his former battle-brothers to their unlife, so that he could release their tortured souls. Yet, despite all his grand schemes and designs, he still needed to find the wayward Ahriman, for only he possessed the necessary knowledge of the Rubric to see what he had done reversed.Amon sent out emissaries all over the galaxy chasing rumours, no matter how minor, of the possible whereabouts of the former Thousand Sons Chief Librarian. During his quest, Amon came across other former members of the Thousand Sons. He sent his emissaries to his former brothers in the hopes of enticing them to join his warband. If they accepted, they would become a part of the Brotherhood of Dust; however, those that refused faced the prospect of annihilation -- both themselves and those that followed them.In the meantime, Ahriman had been hiding amongst a Renegade warband of Chaos Space Marines dedicated to Khorne, known as The Harrowing. Somehow the Brotherhood of Dust managed to track the psychic spoor of Ahriman to the warband. Amon sent an emissary named Tolbek, a former Thousand Sons Legionary and member of Ahriman's cabal of sorcerers. An adept of the Pyrae Cult in the long-broken traditions of Prospero, Tolbek had been one of the first to join Ahriman's cabal. Tolbek had played his own part in the casting of the Rubric that destroyed their Legion and had shared in the casters' banishment.Tolbek, escorted by a pair of Rubric Marines, went over to The Harrowing warband's vessel, the Blood Crescent, to entreat with the warband's leader Gzrel. During the subsequent audience aboard The Harrowing's flagship, Tolbek devised the true identity of Ahriman, who had been masquerading as a lowly sorcerous initiate named Horkos -- a Heretic Astartes who was looked upon with contempt by his fellow Renegades as the lowest of the low and an oath-breaker.Recognising Tolbek, and realising his identity had been compromised, Ahriman unleashed his suppressed sorcerous abilities against both his allies and the Thousand Sons sorcerer. After killing the majority of The Harrowing's leaders, Ahriman was confronted by Tolbek. Ahriman telepathically invaded Tolbek's mind, attempting to determine why he had been sought out. But the cunning sorcerer immolated his own mind, attempting to pull Ahriman's psychically-linked mind into oblivion with him. Ahriman just barely managed to escape Tolbek's insidious trap and the other sorcerer died as his body erupted into flames, immolating itself into a pile of ash.Before the Chaos Space Marines aboard the warship Tolbek had arrived on realised that their master was now dead, Ahriman took command of the vessel for himself and fled into the Warp. During Ahriman's quest to determine who had sought him out, Amon sent numerous minions to do his bidding, including Warp creatures and a half-Daemon Prince, all of which failed to kill the potent exiled sorcerer. Despite Amon's best efforts, Ahriman managed to discover his former brother's location and infiltrate his fleet.Unfortunately, before Ahriman could launch a surprise assault upon Amon, he was betrayed by the mistress of the ship he had stolen, his location compromised. Ahriman managed to emerge victorious after battling against three of Amon's Chaos Sorcerers, but was badly wounded during the fighting. Amon eventually appeared in person and subdued the wounded Ahriman with powerful wards of binding and hexes, and brought him aboard his flagship, the Sycorax. While imprisoned, Amon convinced Ahriman to give him the invaluable information he desired so that he could undo the Rubric, and Ahriman finally agreed.Ahriman's allies came to rescue him and they managed to effect his escape, but the former Chief Librarian was soon confronted by the angry Amon, who unleashed a powerful psychic attack. During the ensuing duel, Ahriman revealed the final secret of the Rubric to his former brother -- it was a part of all Thousand Sons, bound into their very beings -- the Rubric ran through them all, linking them, sustaining them. And the deadly power to manipulate it remained in Ahriman's hands.Unable to pull his mind away from Ahriman, the Chaos Sorcerer caused Amon to spontaneously combust from within, unleashing the powerful psychic energy of the Rubric that had been bound into his own flesh with the casting of the arcane spell. Amon's armour came apart, each component pulling away from the other, spilling grey dust into the twisting wind.The vortex of power he had unleashed to kill his brother enveloped Ahriman and lifted him into the air, the separate pieces of Amon's armour aligning themselves over his unarmoured, splayed body. Then, one plate at a time, they slid into place over Ahriman's flesh. Finally Amon's horned helm slipped over Ahriman's skull. The minds of the still-living sorcerers of the Brotherhood of Dust teetered on the edge of indecision. The undead Rubricae simply waited.Raising his hands, Ahriman summoned magical flames from the floor which engulfed the red lacquer of the armour of every Rubricae and sorcerer of Amon's Brotherhood of Dust. Then the flames suddenly flickered blue, and the red-and-silver armour became instead a sheen of polished sapphire.Ahriman then looked across the ranks of newly transmuted blue power armour. Slowly, he knelt and bowed his head in recognition of his own sins against the Thousand Sons. He then assumed the mantle of leadership of the Brotherhood of Dust, including its massive fleet and army of followers, mortal and Heretic Astartes alike.It is not known if the former Brotherhood of Dust is the same warband, now known as the "Prodigal Sons," that Ahriman currently leads in the 41st Millennium.