Warning: SPOILERS for The Flash episode "Escape From Earth-2" lie below! Don't say you weren't warned!
Perhaps one of the biggest takeaways from Tuesday's episode of The Flash was Zoom's other prisoner besides Barry and Jesse. There have been many theories about who is behind the iron mask, but one thing is clear: it's not Leonardo DiCaprio.
Theories on this mysterious prisoner's identity have ranged from the *real* Jay Garrick, to Earth-2's Eddie Thawne, and potentially even a future Jay. I have my own theory on who is behind the iron mask, but before I reveal it, let's run through why it can't be some of the other potential candidates.
Why the man in the mask isn't Jay Garrick
When we first see the man in the iron mask, he uses an old POW tap-code to spell out "Jay" before Zoom appears and orders him not to communicate with the other prisoners again. In addition, when Barry says that Jay is on his Earth, the man bangs his head against the glass in frustration. Some people have taken these two facts together to mean that the man in the mask is actually Jay Garrick and that the "Jay Garrick" we know and love is an imposter. I disagree with this theory because if it was Jay, he would not be willing to stand up to Zoom, as proved by Wells' affirmation that Jay is a coward. Another reason I dispute the man being Jay is that I think he spelled out Jay not to reveal his identity, but rather to question why Barry appeared to rescue him rather than his own Earth's Flash. Now that we've run over why the metal-faced man can't be Jay, let's look at some other possibilities for who it can't be.
Why the man in the mask isn't Eddie Thawne
So why couldn't Eddie Thawne be the mysterious, faceless inmate of the evil speedster? After all, he's one of the only characters whose Earth-2 version has yet to appear on screen. Well, the two main reasons Eddie can't be the man in the mask is that either (a), the man in the mask IS a speedster, or else (b), knows enough about them to be of some value to Zoom, neither of which describe Eddie, unless on Earth-2, he's secretly a metahuman. Secondly, if Eddie is not a metahuman on Earth-2, there would be no reason for Zoom to have not simply killed him. Zoom has proven that he's not above unprovoked murder, so the fact that this prisoner is still alive indicates that whoever he is, he has something Zoom wants that can only be obtained if he is alive. But is there anyone else the man in the mask couldn't be? As a matter of fact, there is.
Why the man in the mask isn't Earth-2 Wally West
There are a couple important reasons why the man in the mask can't be Earth-2's "Kid Flash" Wally West. The first (and most obvious) reason is that whoever the man under that mask is, he's clearly not the same ethnicity as Wally West. Secondly, even if the ethnicity was right, Wally obviously is not a metahuman on Earth-2 or else Jay (and prezoomably Zoom... yes, I really just made that pun) would have known about him. So, if not Jay, Wally, or Eddie, is there anyone else we can eliminate as a potential candidate?
Curveball answer: why the man in the mask isn't Earth-2 Rip Hunter
We know that Eobard Thawne briefly references Rip Hunter in the season 1 finale, but it's pretty unlikely Zoom would know (or care, for that matter) about him. I mean, yes, a guy who can travel through time could cause problems for a man bent on world domination, (hello, Vandal Savage), but Rip would never allow himself to be captured in such a way. And even if he did, I'm sure his team (whoever they consist of on Earth-2) wouldn't have too much difficulty coming to locate him, what with him being their leader and all.
So, who is the man in the mask?
Now that we've effectively established pretty much every possible candidate for who can't be under the iron mask, it's time to discuss the man I think is. However, there's one important factor that this entire theory hinges on: Zoom's identity. In order for this theory to work Zoom has to be the one character whose Earth-2 doppelgänger has yet to appear on the show: Eddie Thawne. If Zoom turns out to be any other character, this entire theory will go up in a puff of smoke. Because I personally theorize that the new "man in the iron mask" is... drum roll please... EARTH-2 Eobard Thawne!
Now you might be wondering why this theory depends completely on Eddie being Zoom. The reason is simple. If Zoom is Eddie, he knows that Eobard, as his descendant, would be able to identify him. And Zoom's entire reign of terror is based on the fact that no one knows his true identity, meaning the police are being menaced by a faceless and seemingly all-powerful enemy. If, however, someone came along that could reveal his identity, (whether by accident or intention), Zoom's entire empire would collapse around him. Eobard likely lost his speed on Earth-2, stranding him in the past, just like his counterpart on Earth-1. So, if the man in the mask is actually Earth-2's Reverse-Flash, (who is also a villain), why would Zoom want his speed? Remember what Jay said to Barry way back in the beginning of season 2? "He wants to be the only speedster around." But in this episode, Zoom tells an incarcerated Barry that he needs him alive in order to sap his speed from him. So, why then, has Eobard not already been killed by Zoom? I believe that Zoom realizes Eobard has lost his speed and is trying to figure out how he can get it back long enough for Zoom to steal it for himself.