Chaos
Chaos thrives within Order and at the birth of the Imperium of Man, half the Emperor's Legions turned against him in a civil war known as the Horus Heresy. Aligned with the forces of Chaos, those same traitors continue to launch their Black Crusade out of the Eye of Terror thousand years after their defeat. The price of power and immortality cost the traitors their sanity and were bestowed with chaotic mutations both hideous and deadly.