Chaos Space Marines
The Chaos Marines are also known as the Traitor Marines and Traitor Legionnaires. They were once part of the original selection of Space Marines to help unite the Imperium. Under Warmaster Horus, however, they were corrupted by the forces of Chaos. They followed him in his revolt against the Emperor and fought against their former brothers throughout the Horus Heresy. When Horus was defeated at the Battle of Terra, the Chaos Marine legions were imprisoned in the chaotic and unstable Eye of Terror. From there they fight the Long War, continuing their revolt against the Imperium, and waiting to exact their vengeance.