There are few tropes in superhero fiction as worn out as "good guys fighting each other, but then, later, they make up and fight the bad guys." And with good cause! It offers a transgressive thrill (Aw, hell no, you think to yourself as you watch, that's not supposed to happen!) without destroying the overall moral alignments of the story. We already had one such tussle in the first Avengers movie, when Thor got all pissy with Captain America and Iron Man before agreeing to join forces.
But from the looks of the new trailer for Avengers: Age of Ultron, we're about to get a much more invigorating bit of temporary infighting: The Hulk versus Iron Man in a Really Big Suit of Armor. (This kind of armor is nothing new in the comics, where Tony Stark has had so-called "Hulkbuster" outfits for years.) But why? Here are five educated guesses about what will drive two of Earth's mightiest heroes to go mano-a–Iron Mano.
1. Bruce Banner is mad at Tony Stark for ruining everything.
We've long known that Iron Man is going to be the one responsible for building the murderous sentient robot Ultron, or at least the foundational technology that breeds him. This trailer also gives us a taste of Tony Stark's holier-than-thou reasoning for the creation of a drone army. ("This vulnerable world," he says in voice-over, "needs something more powerful than any of us.") It stands to reason that Tony's missteps may eventually infuriate mild-mannered Bruce Banner to a point where he thinks Ol' Shellhead needs to be neutralized. Given that the trailer also features Thor choking Tony and saying, "You've meddled with something you don't understand," justified resentment seems to be on the menu for the world's premier superteam.
2. The Hulk is under mind control.
We don't know what the movie version of Wanda Maximoff — a.k.a. the Scarlet Witch — has in her power set. To be honest, even the comics version has long had a vaguely defined list of abilities. But given that comics-Wanda has reality-altering powers and a general tilt toward all things magical, it stands to reason that movie-Wanda could have a degree of mind control. As Entertainment Weekly's Anthony Breznican points out, Hulk appears to have red eyes during the fight ... and Wanda has them, too. We've already been told that Wanda and her brother Pietro spend some portion of the movie on #TeamUltron, so could the Hulkster be under the influence of eeeeeevil? Which brings us to our next theory ...
3. The armor has been hacked by Ultron.
It could be that the forces of nastiness have taken control of Iron Man and not the Hulk. The trailer goes out of its way to show us that Tony is, indeed, inside the supersize armor (we get that patented screens-surrounding-the-floating-face-of–Robert Downey Jr. thing during the sequence). But that doesn't necessarily mean he's in control of the armor. We already know Ultron is able to control an army using Stark-designed technology, so it's entirely possible that he can hop into the CPU of the Hulkbuster. This would be an eyeroll-inducingly clichéd plot development, given that hacking Iron Man's armor while he's still in it is a gimmick that's been used countless times in the past. And speaking of clichés ...
4. The Hulk has gone berserk.
It would be extremely dull if this were the reason, but then again, it's a plot development that's been used in 800 bajillion Hulk story lines in the past. At some point in the movie, Banner could get ticked off so much that he loses all self-control and the Hulk just starts going straight-up cuckoo-bananas. Much like a Dustbuster in an apartment full of cat hair, the Hulkbuster could be brought in to clean up the mess.
5. It's all part of the plan.
Tony Stark is nothing if not a schemer. He's the closest the Marvel Cinematic Universe has to Batman: a non-superpowered human who works closely with all the superhumans but never totally trusts them and always has a backup plan. Perhaps Tony has a so-crazy-it-just-might-work tactic that involves him fighting the Hulk. Maybe he's creating a diversion. Maybe Banner helped develop the plan and knew it'd involve his alter ego getting beaten up. Or maybe (and this is something that's been done a few times in comics, perhaps most memorably in the climax of Mark Millar and Bryan Hitch's The Ultimates, Vol. 1) one or more Avengers decided to use a berserk Hulk as a melee weapon against a sea of bad guys. You can't exactly flip a switch to turn the Hulk off, so maybe the Hulkbuster armor was on call to settle things down after Big Green had done his job — or, you know, after the best laid plans of iron mice and iron men went awry.