A sergeant major in the UNSC Marine Corps, Avery Johnson serves as a supporting force to the Halo series's primary protagonist, the Master Chief. Thus he is a participant in many of the major battles of the Human-Covenant War. He survives many rough situations, but at the end of the war, he is killed by a rampant AI monitor when he tries to fire a Halo that is still under construction.
Sergeant Johnson makes an appearance in all 3 of the core Halo games, though as an unplayable NPC. With the release of Halo 3: ODST, players are finally able to play as him.