Ahzek Ahriman is a warrior of the Thousand Sons Legion and the greatest Sorcerer within their ranks. A Terran marine, Ahriman rose through the ranks of his legion to become their Chief Librarian and preeminent master of one of their psychic disciplines: precognition. Surviving the various battles of the Great Crusade, Ahriman found himself at the centre of the events that would lead to the fall of the Thousand Sons and their collective descent into the clutches of Tzeentch, Chaos God of sorcery and change, during the Horus Heresy.
His actions after the Heresy, he joined Garro of the Death Guard and fled with him.
Ahzek Ahriman was born on Terra, among the wealthy tribes of the Achaemenid Empire, whose kings had allied with the Emperor during the Unification Wars early. Because of this alliance, Ahriman's tribes were largely spared the horrors of the atomic wars and invasions of the Unification period. Following the Emperor's victory and Terra's alliance with Mars, Ahriman and his twin brother Ohrmuzd were selected to be inducted into the ranks of the Legiones. The Ahriman brothers traveled to the stars alongside the Emperor and his legions as part of the Great Crusade, but five years into the expedition the Thousand Sons legion began manifesting psychic abilities, and with the manifestations began the terrible flesh-changes. Over time, the problem became so severe that many voices throughout the Imperium began suggesting that the Thousand Sons be disbanded. However, when the Crusade reached Magnus upon Prospero not long after, the Primarch of the Thousand Sons was seemingly able to eradicate the threat of the flesh-change; although only a fraction of the affected marines survived the mysterious process. One of those who perished was Ohrmuzd Ahriman, whose passing instilled in his twin both great grief and a great dread of the flesh-change. In remembrance of his brother, Ahzek had Ohrmuzd's pendant (the twin of his own, both gifts from their mother) worked into the shoulder-guard of his armour.
Ahriman rose to hold the positions of Chief Librarian of the legion, captain of its 1st Fellowship, commander of the elite Sekhmet and leader of the legion's most powerful cult, the Corvidae, all at the same time. Despite this impressive record, little is currently known of the bulk of Ahriman's career as a legionary. The earliest mention of him is a note of his five years' secondment to the Word Bearers legion, where he found himself uncomfortable with their expressions of belief in the Emperor's divinity without a knowledge-base to back it up. Despite this period being one he thought of unhappily, Ahriman did consider that he had become friends with the Word Bearer named Erebus during it. He is also on record as being in favour of the assignment of remembrancers to the Crusade forces, believing the documenting of his legion as being one way in which the wider body Imperium could learn to understand - and therefore no longer fear - the psyker.
The earliest detailed mention of Ahriman in historical records currently known of is during the Aghoru campaign, a compliance action carried out by the Thousand Sons of the 28th Expedition towards the close of the second century of the Great Crusade. During this campaign, Ahriman is noted to have risked his Primarch's displeasure by leading a search team for him after Magnus made himself absent from the legion, despite Magnus' prior insistence that he was not to be disturbed. This is the first time he is known to have both mistrusted the judgement of his Primarch and ignored his wishes. Towards the end of the campaign, when a contingent of Space Wolves arrived to convey a message to Magnus from Leman Russ, Ahriman found himself falling into an association 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 like-minded individuals, but which would later prove treacherous.
His perceived fledging kinship with the Rune Priest proved helpful however, when both the Space Wolves and the Thousand Sons were forced to engage in combat with xenos weaponforms and hostile denizens of the warp before leaving Aghoru. Around this time, Ahriman was charged with inducting the remembrancer Lemuel Gaumon into the ways of the Thousand Sons by Magnus the Red, in an overt attempt to develop Gaumon's own psychic abilities and help spread understanding of Magnus' philosophies. Ahriman took Gaumon on as his Probationer, and spent a significant amount of time illuminating and training the remembrancer throughout the period leading up to the Burning of Prospero. This training included taking Gaumon along on combat missions during the pacification of Heliosa, where Ahriman was present for the return of the flesh-change in his legion and the execution of the afflicted Thousand Son by the Space Wolf Primarch, Leman Russ. The return of the flesh-change to the Thousand Sons after Magnus had previously promised that he had banished its danger forever made a deep impact on Ahriman, his feelings of dread at the possibility of mutation and hurt betrayal caused by his Primarch's inability to protect the legion being so strong that Gaumon was able to detect them.
Soon after this, the Legion turned to Chaos and the loyal elements were destroyed on Propspero, Ahrimans is thought to be the last loyalist of the Legion.