A deadly, dim-witted bounty hunter, Lobotomaxx is nobody's friend - especially not Predacon's, 'cause he cut off part of Lobotomaxx's brain. He's still kinda sore about that.
Devil's Due G.I. Joe vs. the Transformers comics continuity
Lobotomaxx discovered the backwater planet of Earth, and recruited Carcass and Predacon to help him pillage it. Upon arriving in Earth's solar system, however, all three would-be raiders and their ship were devoured by Unicron.