Ahriman

Ahriman was the greatest of Magnus's sorcerers save the Crimson King himself, Chief Librarian of the Thousand Sons and a master of the Corvidae, the cult devoted to the divinatory arts of seeing what was yet to come. Brilliant, proud, and utterly devoted to the pursuit of knowledge that defined his Legion, he stood among the innermost circle of Prospero's adepts and was widely regarded as the natural inheritor of his primarch's boundless learning. His gifts of foresight were formidable, yet even he failed to see the full shape of the doom bearing down upon his home.

At the burning of Prospero, Ahriman fought amid the wreckage of everything he had believed unassailable, and the trauma of that day, together with the horrors that followed the Legion into damnation, planted in him a resolve that would one day reshape the Thousand Sons forever. In the Heresy era, though, he remained what he had always striven to be, the perfect scholar-warrior of the Fifteenth, his loyalty to Magnus absolute and his faith in the redeeming power of knowledge not yet curdled into the desperate, fateful hubris for which later ages would remember his name.