Drift was not always an Autobot. Once fighting for the Decepticons, he defected to the Autobots when he found out the error of his ways. Abandoning the ways of the gun, he changed his name (Dreadlock) to Drift, and wielding the Great Sword that can destroy any target, at the cost of some energy drained from his spark.
After some time, he got killed along with Ratchet and Hound by a Con called Helex. Helex assumed he died, instead he was instead transported to a different world