Gunbarrel is a Targetmaster. He was sad because he was left alone on Cybertron, and in a depression because all of his friends died in the First Great War. Jazzimus Prime found him, sometime when he, the Anibots, and three other Autobots came on Cybertron scouting for Stasis Pods that were still remaining. Jazzimus talked to him, for a bit, and then took him as his gun, as he felt sad for the Mini-Con. Gunbarrel was reluctant to become a Belligerent in this war, but Jazzimus told him that he'd avenge them. Gunbarrel joined the Prime, and transformed.