>>213029631He's a dickhead from the future who stole some technology and went back in time because he thought he'd be able to cakewalk his way to fame and fortune as a super hero, but he's just kind of an asshole, and the DC universe is full of other super heroes.
Most famous for teaming up with Blue Beetle, another "why is this guy here?" hero, they work pretty well together.
There's a pretty good episode of the justice league unlimited that focuses on him being stuck on perimeter duty.