Halo 3
The main character of Halo 3 is Master Chief. Master Chief is a super soldier, the last surviving member of the Spartan Project. The Spartan Project was started by humans to genetically, using genes, make soldiers who were stronger, faster and tougher than any normal human. Another character from Halo 1 and 2, controlled by the second player in a co-op game is Arbiter, the leader of the alien Elites. In Halo 2 he is an enemy but in Halo 3 he joins forces with the humans. Other returning characters include the veteran human soldier Sergeant Avery Johnson, the AI Cortana, the robot 343 Guilty Spark and the Gravemind, the dangerous leader of the Flood.