From Halopedia, the Halo wiki
Vallen was an inhabitant of Harvest. He was a recruit of the planet's Colonial Militia and fought in the First Battle of Harvest. He was older than fellow recruits Habel and Jepsen. While defending Harvest Reactor Complex which housed Mack's AI core, He, Byrne, Habel and Jepsen faced off against 3 Brute Choppers. Though the other three made it through the safety of Mack's core building, Vallen was killed by a Chopper's spikes (via running him over) just a few meters before the door of the building.
List of appearances