The Flash Season 2: Flash vs Zoom

The big mystery for much of season 2 was the identity of the evil speedster in the black suit: Zoom. Supposedly he came from Earth-2, where he was an enemy of that world’s Flash, Jay Garrick. The singularity opening at the end of The Flash season 1 supposedly brought Jay to Earth-1 and made Zoom aware of Barry’s existence.
The Flash Season 2: Flash vs Zoom