There are a lot of theories about who Zoom could be and just like everyone else, I have my own opinions about who it could be. Here's my list.
1. HUNTER ZOLOMON: Hunter was a cop who got into an accident that gave him the power to manipulate time and make it seem like he has Superspeed. He became a villain of Wally West's version of the Flash and was Wally's version of the Reverse Flash.
-WHY IT'S HIM: In the comics, Hunter Zolomon IS Zoom so it's a no brainer that he could turn out to be Zoom here in this TV show. Plus, now that we know Hunter actually exists in the Flash universe, he is now my #1 suspect.
-WHY IT'S NOT HIM: We still don't know much about this version of Hunter Zolomon. He was adopted but not much else beyond that. Was he a cop before moving to Central City? Does he have ANYTHING in common with his comic book counter-part? Being from Earth-Prime, Hunter would have to travel to Earth-2 before any portals formed, become Zoom and then come after Barry. That presents it's own problems right there, but like I mentioned previously, Zoom's powers in the comics are Time Manipulation, so perhaps Hunter CAN be Zoom and be from Earth-Prime. Stranger things have happened.
Plus, we have to remember the writers have proven to be unpredictable. In season 1, it was OBVIOUS Dr. Wells was the Reverse Flash and that's why I didn't go for that choice because it was too obvious. But then it turned out to be true and the writers didn't do anything to make the audience doubt it. Then in season 2, the writers introduce the Fake Dr. Light, but instead of making her Kimiyo Hoshi (or Arthur Light) like they were supposed to, she turned out to be Linda Park. And now with Zoom, the writers are doing an excellent job making everyone think this guy could be Zoom, no this other guy could be Zoom.
So, in the end, Zoom can turn out to be anyone. But let's hope the writers have some semblance of respect for the source material and have Zoom be who he is SUPPOSED to be and that is Hunter Zolomon.
2. EDDIE THAWNE: We all know Eddie's story, no need to repeat it here.
WHY IT'S HIM: Prior to the revelation of the Reverse Flash making his "impossible" return, Eddie was pretty low on my list. I didn't think it likely but it was possible Eddie could be Zoom. And now that the Reverse Flash has returned, Eddie has moved up my list. Why? I already explained this but I'll explain it again.
Eddie Thawne's body was sucked into a singularity and although Eddie shot and killed himself, time travel is often connected with singularities. It's FULLY possible the singularity could have changed him and he ended up somewhere on Earth-2's past and got revived by some unknown technology and became Zoom. I speculated that maybe we haven't seen any indication on who Zoom is because Eddie needs the suit to live much like Darth Vader needed his to live. Eddie has a lot in common with the comics version of Hunter Zolomon, so it's not out of the realm of possibility that Eddie could be Zoom.
Plus, in order for the Reverse Flash to even be alive, Eddie HAS to be alive somewhere. That's the only explanation that makes sense as to how and why the Reverse Flash still exists.
WHY IT'S NOT HIM: Eddie shot and killed himself, it's pretty hard to come back from that. But then again, Reverse Flash was erased from existence and he came back from that...
Plus, I heard a rumor that Rick Cosnett didn't get along with the showrunners and if that rumor is true then the likelihood that Eddie is Zoom is about zero.
3. FORCE of NATURE: I have speculated that Zoom could be more of a force of nature than anything else and has no secret identity.
-WHY IT'S TRUE: When I look at Zoom, I think of a character who is an obvious amalgam of two different characters, perhaps more. He has some things in common with the Black Flash but also with Zoom in the comics. He wants to be the only speedster out there and that sounds a lot like someone who has taken a few pages out of the Black Flash's book.
-WHY IT'S NOT TRUE: Notice Zoom's costume, it may be black but it's also very similar in design to Barry's own costume. Plus, Harry said that he created Zoom and that Zoom WAS human once.
4. Earth-2 Barry Allen: We don't know anything about Earth-2 Barry.
WHY IT'S HIM: In the comics, Barry actually becomes the Black Flash. Not only that but Harry says he created Zoom. Well, guess who created the Flash on Earth-Prime? Dr. Harrison Wells. Coincidence? I don't think so. Two characters who got their speed because two men named Dr. Wells created the Flash and Zoom? There's got to be a connection there.
WHY IT'S NOT: Barry is skinny as a toothpick (seriously Grant, ADD SOME MUSCLE) and whoever is playing Zoom looks like a big guy under that suit. Sorry, but it cannot be Barry even if he's from Earth-2.
5. Fake Wally West from Earth-2: We don't know anything about Fake Wally from Earth-2.
WHY IT'S HIM: If the writers wanted to throw us a curveball, this would be it. It would shock pretty much everyone and come out of left field. And given the unpredictable nature of the writers, this is exactly the kind of thing I'd expect from them. In the end, I'll hate the revelation because it doesn't stick with the original source material.
WHY IT'S NOT: Fake Wally suffers from the same problem Barry suffers from. Too skinny.
And here is a list of people who just don't quite make the list simply because too many things run against the possibility it could be them.
1. Jay Garrick: Ok, so he pretended he lost his speed but didn't and he's undercover right now even as he gets close to Caitlin and could kill Barry at anytime? Plus, we all know Jay isn't a bad guy in the comics. But then again, his Earth-Prime counterpart IS Hunter Zolomon. I'm sorry, this theory is just silly.
2. Earth-2 Henry Allen: John Wesley Shipp has stated himself he has no interest in putting on the Flash suit again. Even if it wouldn't be the suit he wore in the 90's Flash series, John is just not interested. This is a case where money cannot talk. And besides, we don't know if Earth-2 Henry Allen even ended up in jail. In fact, we don't know anything about him. So, until I am given a plausible reason to put him on my list, he remains off of it. There is simply no way Earth-2 Henry Allen is Zoom.
3. Earth-2 Eobard Thawne: This would be pretty much repeating the same villain we saw in the first season even if it's a different version of him. Sorry, I just don't see this one happening at all.