In Halo 3: ODST, the player-controlled Orbital Drop Shock Trooper is known as the Rookie.
The Rookie is a newly assigned member of the ODST squad deployed into New Mombasa during the events surrounding Halo 2. After the squad’s drop goes wrong, the Rookie wakes up alone and explores the city at night while searching for clues about the missing team members.
Unlike Master Chief, the Rookie is an ordinary human soldier rather than a Spartan. The game uses that perspective to emphasize the vulnerability of ODST troops and the danger of fighting Covenant forces without Spartan armor. Players also control other squad members during flashback missions. Although the Rookie is the central playable character, the game does not reveal a personal name for the character.