The Emperor uses the Space Marine Legions to conquer the scattered human worlds of the galaxy, uniting them under the Imperium of Man in the Great Crusade. Over time, two Primarchs would disappear from Imperial records while others would have difficulties with their father and each other. As the campaign drew to a close, nine Primarchs and their Legions convert to the worship of the evil Chaos Gods, rebelling against the Emperor and sparking a galaxy-wide civil war known as the Horus Heresy. During the final hours of the war, Horus Lupercal, the Emperor's favourite Primarch-turned-traitor, and the Emperor fight each other in a duel. Horus is killed, but the Emperor himself is so badly injured, he is placed on permanent life support.