Leonardo Darrell Simmons, bettern known as "Leo" amongst peers, was an Orbital Drop Shock Trooper who served as an enlisted member of the UNSC Marine Corps, and later served as an Officer in the UNSC Navy during the Human-Covenant War. He was rewarded a Navy battlefield commission to the grade of Ensign by the Office of Naval Intelligence during the Battle of Sydney in 2552. He continued service in the UNSC Navy post war until his eventual retirement in 2598.