From Halopedia, the Halo wiki
Mission aboard Mona Lisa
He was assigned to serve under Sergeant Zhao Heng Lopez when her squad was sent to investigate the prisoner transport Mona Lisa within the debris field of Halo Installation Alpha. Unbeknownst to the Marines, the mission had been commissioned by the Office of Naval Intelligence whose operative John Smith had been secretly researching the Flood parasite on the Mona Lisa.
Soon after a firefight with a group of unarmored Sangheili in the ship's cargo bay, the Marines received orders to purge the Mona Lisa's NAV databases in accordance with the Cole Protocol. They split up into two teams, with Sergeant Lopez's team heading to the bridge and Corpsman Benti's team set to destroy the backup database in the engine room. Gersten was assigned to Benti's team, along with Orlav, Tsardikos and Clarence.
When passing through the ship's recycling plant, the team became under attack by a horde of Flood. Orlav was infected and managed to bite Gersten in the face. After the Marines got to safety in a maintenance room, Gersten began to show signs of Flood infection, and was shot in the head by Clarence without hesitation. His body subsequently reanimated, but Clarence shot him again, killing him permanently.
His name, as stenciled on his chest plate name tag, is misspelled twice in the motion comic adaptation of The Mona Lisa; as "Gestern" in the third episode, and "Gerstern" in the fifth.
List of appearances