'The strength of the Emperor is Humanity, and the strength of Humanity is the Emperor. If one turns from the other we shall all become the Lost and the Damned.'
The Sermons of Sebastian Thor, Vol. XXVII, Chapter LXII
From the twisted region of space known as the Eye of Terror, the Chaos Space Marines launch their devastating Black Crusades against the Imperium. Once valiant and pure Space Marines like those that serve mankind, these foolish warriors rebelled and were forever damned after the wars of the Horus Heresy to eternal servitude to the vile gods of Chaos! Over the years, these cursed traitors and heretics have been mutated and changed by the warping influence of the Chaos powers, but they still carry on their ten thousand year old war against the Imperium!
The Chaos Space Marines themselves are cruel mockeries of the true defenders of humanity, twisted into hideous new forms in servitude of their inhuman masters such as bloodthirsty Khorne Berzerkers and putrid, disease-ridden Plague Marines. When the Chaos Space Marine Legions fled to the Eye of Terror, they also took all their wargear with them, including Terminator Armour, vehicles and Dreadnoughts. This makes them every bit as effective as their sworn enemies, the
Space Marine legions, on the battlefield. Of course, the strange warping effects of Chaos has affected vehicles and equipment as well as men, forging them into near-immortal servants of the dark powers. Now they take to the battlefield alongside hideous Daemons and other cursed creatures of the Warp in an unending war to consume to the entire universe in the gibbering madness of the Realm of Chaos!