Bumblebee is an Autobot from One.
B-127 works in waste management in the lower levels of Iacon, and has done so for a long time. So long that he hasn't spoken to anyone else in a while, and the isolation's kind of getting to him—he's built himself a group of imaginary friends to keep him company, and he talks way, way too much to fill the silence. Even when he's unconscious. Especially when he's unconscious.
His name is kind of clunky, so he's been trying out a few nicknames, like Badassatron; for the most part, people just call him B.
Maybe he'll figure out something better eventually.