Ahzek Ahriman
Ahzek Ahriman (A.K.A. The Sorcerer of the Red Cyclops) is a powerful Chaos Space Marine of the Thousand Sons.
Early Life
He was born among the wealthy tribes of the Achaemenid Empire, whose kings had allied with the Emperor during the Unification Wars. His name and birth region indicate that he is Iranian. He was then inducted to join the Astartes along with his twin brother Ohrmuzd (who later died of severe mutations, making it a dead giveaway to Ahriman and Ohrmuzd, two Iranian deities of Light and Dark--guess which one Ahriman is). He quickly rose through the ranks and became Chief Librarian of the Corvidae (the most powerful cult of the Thousand Sons).
Basically, he is an evil Persian Space Marine reeking of JUST AS PLANNED.
During the Heresy
Rubric of Ahriman
Seeing as to how the Thousand Sons were quickly succumbing to the flesh-change since Tzeentch is the God of change and all, Ahriman attempted to permanently cure them of their mutations. Without Magnus' consent, he, along with a cabal of other sorcerers, cast the Rubric of Ahriman. On the up-side, all the psychics in the legion stopped mutating and became more powerful than they were. On the down-side, everyone else in the legion who wasn't a psyker was cursed to be turned into dust and be sealed in their armor for all eternity, turning them into soulless automatons who are unable to think for themselves. Needless to say, Ahriman went derp.
After Magnus learned of this, he flew into a nerd rage so great that even an Angry Marine would take pause to admire the rage. Magnus was about to kill Ahriman but Tzeentch himself told Magnus that it's not as planned, and so kicked his ass out of Prospero instead and forced him to wander the Chaos Wastes.
Current Status
He is constantly trying to gain entrance into an Eldar library. Not just any library, where he can nerd out like most other geeks, but the mystical Black Library where he can nerd out mystically and become a new major chaos god (which would thus tear reality yet another great big asshole like the eye of terror). And he is constantly failing at that task. To be fair, it is hidden in the ass end of the Webway (which is to say it is hidden in the ass end of the ass end of nowhere). It's also protected by the Harlequins, who are really fucking good at getting their shit done, and the Eldar Laughing God, who still has the full measure of his god-like power, also a master of just as planned (to the point that he can play this dreadfully complicated game on a fairly equal level with the Deceiver, Tzeentch, and the Emperor), and is capable of challenging Slaanesh for the souls for the Harlequin Solitaires and winning. In the end, Ahriman has an excuse, unlike a certain despoiler whose first name is Ezekyle.
In spite of this, he is one of the most awesomely powerful psykers in the galaxy. His miniature can psychic power spam like no one else can, as he is able to throw three powers per turn, which means that he can kill pretty much anything dead with just a mean look. Nerd Rage abounds as to whether the Doom of Malan'tai, Tigurius, Eldrad, Ahriman, or Mephiston is the most powerful psyker alive and not balls to the wall insane or a daemon.