Eobard Thawne was born in the 25th century and a huge fan of the Barry Allen Flash. Using advanced technology, Thawne gave himself super-speed like his idol, and even went back in time to meet him. But in the past, he discovered his fate to become Barry Allen's greatest villain. Driven insane by the discovery, Thawne developed a huge hatred of the Flash and became Professor Zoom, the Reverse-Flash.
Zoom fought the Barry Allen Flash many times, and at one point murdered Barry's wife, Iris (she got better). As Zoom tried to kill his new fiance, Fiona Webb, Barry accidentally snapped Zoom's neck, killing him. Barry would later die himself, but like Iris, would get better. And apparently so has Thawne, as the Reverse-Flash has returned to menace Barry once again.