The unnamed Master Gunnery Sergeant was in charge of Cairo Station's armory, and was a non-commissioned officer. He helped John 117 get used to his Mark VI armor through training and testing his shields.
Shortly after John 117 arrived at the Cairo Station, the Master Gunnery Sergeant fitted him with the Mark VI armor that Maria-062 had tested earlier. After the tests, John 117 left the location and Covenant forces attacked the station. Elites arrived where the Gunnery Sergeant was, the sergeant attempted to defend himself with a shotgun but was killed by the Elites as John 117 returned.