Drifter has never been what you'd call a team player. He prefers to operate alone, rather than as part of a unit. His original four man team? He's the only survivor. And their designations were RC-3631 "Sparks", RC-3632 "Servo", and RC-3633 "Detox". Making him the "older brother" who failed to protect them. He and his team were caught in the underground tunnels on Geonosis when the ground collapsed. Despite their best efforts to fight their way out, only Drifter survived. Since then, Drifter preferred to work alone, not wanting a new team. But unfortunately for him, Command only allowed that for so long. So that's how he came to join the 11th.