Chaos Space Marines

Chaos Space Marines is a word used to describe the many heretical legions of former Space Marines that betrayed the Emperor during the Horus Heresy and became servants of the Chaos Gods - they come in many forms and tend to have Chapters that are devoted to certain chaos deities, they are only truly unified in their hatred of the Emperor Of Man and their desire to help Chaos become the ruling power of creation via acts of unspeakable evil - they are a playable army choice in Warhammer 40,000 and also serve as major antagonists in the related media.