Sentinel Prime is a member of the Cybertron Elite Guard under the command of Ultra Magnus. Sentinel has a history of rivalry with Optimus Prime, who attended the Autobot Academy with him. In his academy days, he was somewhat of a maverick, leading the more responsible Optimus to refer to him as a "walking malfunction." Of course, he's the one that ended up on the Elite Guard while Optimus was sent off to repair space bridges, of which fact he's all too fond of reminding his former classmate... despite the fact that it was only because of Optimus who got the position. He also has a bit of a superiority complex toward non-guardsmen Autobots, not to mention that he's intensely organic-phobic.