Multiple universes, doppelgängers, time travel, alternate timelines; all of these factors add up to impossible answers, to which we can only give our best guesses.
So Season 2 of Flash started a few weeks ago and it wrapped all the problems of the first season into a really sweet knot. But it gave us a lot more questions, like "how can this reality still exist if Eobard can never be born? He won't come back in time, so he won't affect the timeline and create the Flash?" Here's a quick answer: This Earth, since the black hole appeared, has been connected to the multiverse so, as long as people from other Earths live on "Show-Earth," it can't disappear. That's my theory at least. I also know a lot of people are already talking about the "Zoom topic," but I would like to bring my ideas to the table, even if they're not really new or exciting.
Now onto the question of the post: Who is Zoom? Seriously, who is he? If they follow the comics, it should be Hunter Zolomon, but I doubt it. The showrunners already made Reverse-Flash = Eobard Thawne, so I don't think Zoom is going to be Zolomon, I think they're going to make a little twist this time. So who is Zoom?
The first person we (as a simple audience and not comic book fans) probably think about is Barry. I mean, if on Earth-1, Barry is the Flash, on Earth-2 he might be Zoom. But when we stop to think about it, it doesn't make too much sense. Zoom, whoever he might be, is a lot more muscular than E-1 Barry. If we take as fact that the doppelgängers are physically exactly the same, Barry can't, by any means, be Zoom. I mean, look at Zoom next to the Flash, the physical difference is striking!
See? They don't look alike at all. Barry is thin, whereas Zoom is bulky as heck. The suit, however has a lot of similarities. Both suits are made of the same fiber, both have that weird pattern on the side (like ribs), and both have those lines which, I suppose, need to be perceived as bolts of lighting.
So, if it isn't Barry, can it be Eobard...? No, he already was Reverse Flash in the first season. I really don't think he's going to be the bad guy one more time. That would be a really lousy decision on the writers' part; and besides, RF's suit doesn't look at all like Zoom's. Eobard has two overlapping pauldrons. Zoom has none of that.
This one here is weird, at least for my taste, but apparently a lot of people like it, including some of my friends and also my favorite Reactors on Youtube. I can't blame them, though, it does pack in a whole lot of coincidences. What's this theory, I hear you say? Here it is.
What if Henry (Barry's father) were Zoom? Pretty weird, right, but first let's take a look and compare them both and see if they have anything in common.
He looks like a potential candidate on the physical side. But is he Zoom, though? Let's take a look at some more hints, shall we? Remember the end of the first season, when Barry goes through the SpeedForce and sees visions of the past, future, and present all at once? Remember the moment where we see Barry in jail, instead of Henry?
What if that isn't from an alternate timeline, but from another universe, say Earth-2, where Zoom is? What if Henry, instead of Barry, got powers and then Barry got in jail, which is exactly the reverse of what is happening on E-1? Because you see, in a E-2 flashback, while we're with Dr. Wells, we see on the TV that Robert Queen (who is dead on E-1) is the Arrow on E-2.
So what if E-2 Henry's story was similar? Barry ends in jail, Henry gets the speedforce powers = Oliver is dead at sea, Robert is the Arrow. That's the complete opposite of the E-1 situation. Therefore, if we take into account the physical appearance, and the E-2 spatiotemporal context, Henry looks pretty much a good candidate to be Zoom. But wait, if it is Henry, why would he want kill his own son, right guys? Let's speculate a little more and bring back Reverse-Flash to complete the theory.
Let's say 20 or so years ago (while still being on E-2) RF traveled back in time to kill Barry's mom to traumatize him. That's also what RF from E-1 planned to do, but failed, because Flash stopped him. Let's say, RF from E-2 fulfilled his plan and killed Barry's mom. That would traumatize Barry, but it would fill Henry with rage and hatred towards speedsters, so he would set out to kill Eobard, but he couldn't kill him just like that. He needs to have some sort of power, and then BAM! With the magic of plot and mcguffins, he gets the speedforce, and now nothing can stop him. He kills RF, then he tries to fight Jay Garrick. Please remember that on E-2 there's no RF, why? Because Zoom killed him. Anyway, now is the moment when the black hole at the end of Season 1 comes into play. The singularity opens above Jay and Zoom fighting, and then Henry thinks "Hum, a portal to another world... interesting. Let's see if there's a Flash on the other side."
So now he sends people to kill the Flash, but when he realizes there's no progress at all, he decides to come himself. By the way, there are a few interesting lines in episode 6 'Enter Zoom' and episode 7 'Gorilla Warfare' which could be revealing or just a simple coincidence.
In ep6, Barry says "You wanna be a hero?" To which Zoom answers "Heroes die," and then Barry says "Only if you can catch them..."
Now, in ep7, Henry (everyone presumes he's the good' ol Henry from E-1, but I think he's actually from E-2, so he's actually Zoom) says: "Iris showed me what happened with Zoom... I can only imagine what that must have been for you." The tone of voice he has in that moment is pretty weird. It seems to me, what he's actually saying is "You survived me, impressive. No one has yet." This line is also pretty good, "Yeah, I got a tent. I went fishing everyday. I've had my fill of largemouth bass for a while." Please take note that Henry appears on ep7, which is right after Zoom appeared on ep6. Take note also that, at the end of ep6, Cisco hits Zoom with nanites in order to slow him down. That's why he appears in ep7 as Henry, because he doesn't have his speed. Oh, and what Barry says "Only if you can catch them..." goes hand in hand with the line about fish from Henry.
So, with all that I've said, Henry seems to be the right and definitive choice, but yet, I'm not entirely convinced. There's still another theory, which is also far-fetched and crazy, but considering all the craziness (multiverse, time travel, etc.) it could be possible.
So now, what if Eddie Thawne is Zoom? Seriously, what if he is? I know the showrunners said Rick Cosnett was out of the show for good, but keep in mind that writers have already done that before: saying a certain actor was no longer going to be on a show, but finally he is. What if that's the case for Rick Cosnett? Okay, now let's say he is on the show, what can we use to speculate on to say that he might be Zoom? A lot, actually.
Let's go back to last season. Everyone was saying Eddie was Reverse Flash because his last name is Thawne, then we were proved wrong, when Wells/Eobard came forth as Reverse Flash. So now, at the end of the season when Eddie shot himself, people were speculating that he will return as Cobalt Blue (or Zoom), because he had some sort of necklace/talisman.
Also, do you remember the "time sphere" Barry told Cisco to build?
Yep, this one. Well, Ronnie, who's now dead, said that the tungsten plates would melt the core of the machine, if exposed to the black hole's mass. Wells said to replace the tungsten with.... cobalt. See where I'm going with this? No, not yet? Don't worry, everything should be clear in the end.
The line Zoom says to Barry in ep6, "Heroes die," could have a whole other meaning if Eddie is in fact Zoom. That would mean that Eddie was somehow conscious when Barry ran to the black hole and he noticed that the one to close the breach was Ronnie. The hero (Ronnie) died = Heroes die.
Remember also what Wells from E-2 said about Zoom, "He's human... was." Then Cisco said something about his "Demon claws." Just look at Zoom's suit, please.
Those are signs of something that isn't human, or on the brink of becoming something else. Eddie was half-dead when he merged with the time machine. Tadaa! Eddie is Zoom... but yet it doesn't make any sense either, just look:
Eddie has blue eyes, whereas Zoom has brown-ish, green-ish eyes. The build is kind of the same though. The physical aspect is not really the problem here. Right now, it's the spatiotemporal context. Just think about it. Zoom was already around before the singularity opened on E-2, and Eddie was still getting sucked inside the black hole around the same timeframe.
So right now, it's anyone's guess really. Some are even saying E-2 Joe might be Zoom. I think it's just going to be a new character, but it's always nice to theorize.