Finally, the big reveal of Zoom’s identity was made at the end of the last episode – he is apparently another version of Jay Garrick. All the speculation about his identity of whether he is Eddie Thawne, Henry Allen or Wally West Earth-2 Doppel-ganger is put to rest for good. Apart from Zoom’s identity, the episode has also confirmed the identity of the mysterious man in the Iron mask who is caged in Zoom’s lair as well as the Jay Garrick who was killed by Zoom. He is also Jay Garrick but the Earth-1 version of it. He is the original doppelganger of Earth-2 Jay Garrick on Earth-1. When Jay Garrick showed Caitlin his doppel-ganger on Earth-1, he was deceiving her as he was actually Zoom or Hunter Zolomon whereas the original doppel-ganger is taken and caged in Zoom’s lair.
Hunter Zolomon is a dark version of Jay Garrick with a blue lightning/ speed force. He acquired speed-force as a result of particle accelerator explosion, experimented with sizeable quantities of Velocity-9 drug, got addicted to it which had a negative impact on his mind. He could also be a Cobalt Blue/Malcolm Thawne type of character i.e actual physical twin before the explosion of particle accelerator.
In DC Comics, we have’nt seen the character of Hunter Zolomon since Flash Rebirth, where he is talking to Professor Zoom about his plan to make each other better when they are locked up at Iron Heights. He was the Reverse Flash of Wally West era in the same way Professor Zoom/Eobard Thawne was the greatest enemy of Barry Allen. Hunter Zolomon’s body was broken in a big guerrilla attack and Wally West refused to change the past to fix his spine, so he went to the cosmic treadmill to fix himself and turned into Zoom.