In the last Flash's episode we saw who Zoom's real identity is and we also saw that Jay Garrick is dead, but the one true thing that got our attention is who might this man in the iron mask be?
We saw him in other episodes and also he tried to contact with Flash and Jesse and all we learned from him is that he was showing only 3 words J.A.Y meaning Jay Garrick, but when Flash told him that Jay is okay and he's with them he acted all frustrated and angry.
But when all was over and Barry got away with the others and the Breach was kinda closed when we saw Zoom's Hand coming through the breach and killing Jay.
Then in the next episode we saw Zoom carrying Jay and dropping him in front of the masked man and removing his mask and showing his true identity...
Showing us that he is none else than Hunter Zolomon, Jay Garrick's Earth-1 Doppelganger...
Now we have some crucial questions... Who? What? Why?
Why is Zoom Jays Doppelganger and how come we have never seen him in Earth-1 before Barry Opened the Breaches?
Why is he showing himself to the Masked Person?
Who is the Masked Person and why is he trapped by Zoom?
Well, here's my theory I think that at the time when Jay was talking to Caitlin about how he lost his speed he told us that Zoom didn't take his speed as we all thought, but that he lost it trying to become faster by using Velocity-6 and he said that he made some mistakes and lost his speed and it all went wrong
I think that at that time when he used the Velocity-6 he separated himself creating clones of himself and thus was created Zoom and the Jay Garrick we all saw dead.
Yep, you heard me right I think that the man in the Iron Mask is the Original Jay Garrick without his speed this explains a lot about why he got all frustrated when Barry told him that Jay's with him in his world so Jay's Clone got his speed and tried to defeat his bad clone Zoom but Zoom was stronger and so he lost.