“He’s the most – guy, but a total loose cannon," says Mark Ruffalo of playing Dr. Bruce Banner/The Hulk, "No one wants to set him off except for Iron Man... who just wants to see him pop. It’s funny, there’s a really cool dynamic between Tony Stark and Banner. Banner actually enjoys it, and finds it really refreshing. They’re a lot alike in a strange way. They’re both these kind of scientists who are mavericks, kind of renegades. Banner, for all his mild-mannered mythology, he’s still the dude who was testing some pretty crazy s–t on himself, so he has that rebel streak in him.”
It is also stated that Banner wants to be a member of the team, but that rest of the group considers him a liability. As for keeping the Hulk in check, the duty seems to fall to Jeremy Renner's Hawkeye, who will also share a backstory with Scarlett Johansson's Black Widow.
“[Hawkeye is] the only one who can really take down The Hulk with his tranq tip arrows," says Renner, adding "...The only sort of thing I cling to is the relationship of past experiences with Scarlett’s character, with them both being human. ”
Though Captain America was the hero we saw most recently on the big screen, Chris Evans says that things have changed between his solo film and The Avengers and that we'll see a darker take on Steve Rogers.
“It’s just about him trying to come to terms with the modern world," Evans explains, "You’ve got to imagine, it’s enough of a shock to accept the fact that you’re in a completely different time, but everybody you know is dead. Everybody you cared about.. [E]verybody he went to battle with, all of his brothers in arms, they’re all dead. He’s just lonely. I think in the beginning it’s a fish out of water scene, and it’s tough. It’s a tough pill for him to swallow."
Though the team is going head-to-head with Tom Hiddleston's Loki, Chris Hemsworth reveals that his Thor won't necessarily be the most at odds with his half-brother.
“I think [Thor's] motivation is much more of a personal one," he says, "in the sense that it’s his brother that is stirring things up. Whereas everyone else, it’s some bad guy who they’ve gotta take down. It’s a different approach for me, or for Thor... I’ve been frustrated with my brothers at times, or family, but I’m the only one who is allowed to be angry at them. There’s a bit of that.”