Now as seen in last night's episode, we definitely got to know the identity of zoom. Finally after 15 episodes we got to know that the man behind the mask is jay garrick, or atleast carries the face of jay.
Now here are some of the possibilities that may help us to clarify the buttload of doubts we hold in our minds after the awesome episode.
A) Jay garrick who had been helping the flash, was not jay garrick all along. And the man in the iron mask was trying to indicate this to barry by tapping "JAY" on the glass, by telling that the real jay garrick is the man behind the demonic mask, zoom.
B) Zoom is hunter zolomon from earth 1. It can be hunter zolomon, guys. And maybe he was travelling through the breaches very frequently. He made himself look pretty normal when jay (who we thought jay is) and caitlin went to the park. Maybe it was a part of his plan all along. We cant ignore the fact he had pretty perfect plans because of reverb(the doppleganger of cisco in his team)
C) The man who we think zoom is, that is jay garrick or hunter zolomon isnt actually either of the character. Maybe. He is a man who just took the face of jay garrick. As eobard thawne did with harrison wells in season 1. This again leaves us with many possibilities for who the real zoom is.
Those were some of my theories. Well, Whatever the showmakers decide, will sure contain massive amount of awesomeness in it, for sure!