Ahzek Ahriman is a Chaos Space Marine of the Thousand Sons Space Marine Legion and the greatest Sorcerer they have ever produced.
A Terran marine, Ahriman rose through the ranks of his legion to become their First Captain, 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.[1] His actions after the Heresy - particularly creating and enacting the great spell that bears his name — would result in his eventual banishment from the Legion he had spent most of his existence trying to safeguard. His current status is that of wanderer, apparently fated to quest for something never achievable; understanding of the nature of Tzeentch itself.[2]
Despite the nature of his doom, Ahriman has embraced his quest totally, and no bastion of knowledge in the entire galaxy can be considered safe from his rapacious intellect.[2]