Sergeant Major Avery J. Johnson, (voiced by David Scully) is a Marine who leads human forces against Covenant and Flood assaults throughout the Halo series. Johnson and a few other Marines survive the destruction of Installation 04 and are rescued by Cortana and the Master Chief during the novel, Halo: First Strike.
Johnson is the only human seen to survive a Flood infestation, due to a pre-existing medical condition, known as Boren's Syndrome, that grants immunity to the Flood at the cost of one's mental stability. Boren's Syndrome is caused from high exposure to radiation from plasma grenades. If you completed Halo: CE on Legendary, you were awarded with a cut-scene of Johnson and an Elite fighting over an Assault Rifle. They embrace as the Halo ring detonates around them. In Halo 2, Master Chief asks him how he escaped, and he states that it is classified information. If you read the novels, you find out that he hugged the elite for more than accepting death: he used the elites shields to protect him from Halo's detonation. He held on to the body for life as he floated through space, eventually being picked up by a UNSC ship. In Halo 2, he is awarded the Colonial Cross for his heroic actions, and leads UNSC forces to drive the Covenant from New Mombasa, Kenya after the Covenant take the city during the events of the game. Johnson is the sole character featured in the Halo Graphic Novel story, "Breaking Quarantine", which details Johnson's escape from the Flood in Halo: Combat Evolved. He is also a main character in Halo: Contact Harvest. In Halo 3, he is killed by 343 Guilty Spark when trying to activate the incomplete Halo at the Ark.
In many ways similar to the stereotype of charismatic black Marines found in other science fiction (such as Sergeant Apone in Aliens), some publications found Johnson, though enjoyable, somewhat of a flat character. In an interview for Halo: Contact Harvest, Joseph Staten of Bungie admitted that Johnson was a static character in Halo: Combat Evolved, and that despite the character's potential, "he sort of inherited those caricature aspects [from Halo]." Contact Harvest was a chance "to do right by Johnson, to give him the rich, fully fleshed out backstory he deserves, that we have never been able to give him in the game."