Avery Johnson was a Sergeant Major in the UNSC Marine Corp, serving in both the insurrection and the entire Human-Covenant War. He was born in Chicago on Earth sometime in the late 25th century, and enlisted in the marines when he was nineteen. He was enlisted into the ORION Project just after the turn of the century, which was the predecessor to the Spartan-II program. When ORION was cancelled in 2506, Johnson rejoined the marines, becoming involved in many missions against insurrectionists during Operation: TREBUCHET.
Johnson was assigned to train the Colonial Militia on Harvest after an incident that killed over thirty civilians, which is where he became involved in a first-contact scenario with what became known as the Covenant. After the loss of Harvest, Johnson was involved in many battles throughout the war, including the Fall of Reach, the Battles of Installation 04 and 05, the Battle for Earth, and the Battle of Installation 00. Johnson was eventually killed by 343 Guilty Spark on the Ark after he tried to fire the incomplete Installation 08 and kill the Flood.