Mark Ruffalo’s face is turning red, cords ripple in his neck, and veins pulse on his forehead. He slips out of his desk chair to one knee, howling.

We’re on the set of Avengers: Age of Ultron, but he’s not Hulking out. He’s cracking up. We’re sitting in Ruffalo’s trailer during a break between shots, and someone has emailed the actor a link to a fan-made hoax purporting to show a line of Marvel-themed sex toys.

“There’s the Captain America, very sleek looking isn’t it?” the actor says, scrolling through the NSFW images on his laptop. “There’s the Iron Man. There’s the Thor. There’s Black Widow … And here is the 12-inch, silicone … Hulker!”

I try to convince him to tweet these pics and say: “First look at Avengers 2!”

“Oh, I’d be getting a knock on the door from somebody,” he says.

Back on set as Bruce Banner, he’s also trying not to unleash any bad behavior. Ultron, the sinister artificial intelligence program, is shooting up an Avengers party in Tony Stark’s Manhattan skyscraper, and while the rest of the team battles an array of malevolent ‘bots, Scarlett Johansson’s Black Widow is focused on protecting everyone from the big, green guy.

As the special effects team blows up bottles and other glassware along a bar shelf, the very-pregnant Johansson hurls Ruffalo to the ground and tells him to breathe – and not let the monster come out. If there’s a love story in Age of Ultron, it’s a tentative one between these two.

“In their relationship, she protects him,” Ruffalo says. “She becomes his bodyguard, in a weird way. And he goes with it. I mean, Bruce, he’s a pacifist, man. I want to add a line to this movie after he just smashes the s— out of something as Hulk, I want him to come back and be like, ‘You do know, I’m a pacifist.’”

In our Q&A, Ruffalo talked about what he wants to see if Hulk ever gets another stand-alone movie, and how performance-capture pioneer Andy Serkis (who co-stars in Ultron as Black Panther’s future nemesis Ulysses Klaue) helped him find his inner monster.

Entertainment Weekly: People have been hungering for a return to you as Bruce Banner since The Avengers. They want a solo Hulk movie, and to see him turn up in different films. And you did get a little cameo in Iron Man 3.

Mark Ruffalo: That’s right, that’s right. Robert Downey’s genius. Backstage at an Oscar event.

Oh, is that where that came together? When you werepresenting at the Oscars?

Yeah, we were there and he’s like, “Ruffalo, would you come and do a cameo in Iron Man?… I have this whole idea where I’m telling you the whole story.” And I said, “That sounds great.” And then I left and came back and shot it.

I didn’t realize that was the origin of that.

That was how it happened, yeah.

What is Bruce Banner’s place in the world, place on the team at the beginning of Age of Ultron?

I think you find him about as close to being part of the Avengers as he possibly can be. He’s got his own space, he’s got his own room, he’s doing his own work. He’s not living in squalor and he’s not on the run and he has friends and people who come to understand and figure out how to live peaceably with him. And I think he’s on the way to living quite peaceably with himself, almost foolishly, probably. And that’s kind of where he starts.

Why foolishly?

Well, always lurking in the shadows is this monster that—is it ever really controllable? Does it ever really go away? Is there any real mastery over it?

How has playing the Hulk changed? There’s a big technological component to this performance, and that seems to evolve quickly.

Another really interesting thing, I think, has developed because of the new technology and from Andy Serkis’ input and actual demand that the CGI is just a tool for performance. We were leading towards that in the last one, but he created a space that can be realized with the Imaginarium. Andy Serkis’ mystical, magical Imaginarium.

Imaginarium? What is this?

He basically created a lab, it’s an entire mo-cap facility, but with the attitude that everyone who works there and everyone who’s a part of this place uses mo-cap as a tool for an actor’s imagination to fly without any limitation. So he really leads with “Listen man, this is you, this is your performance, this is not a placeholder for the CGI people to come in and build this character. This is your performance.”

So Gollum and King Kong himself is coaching the Hulk?

He’s there, it’s his deal, it’s his place. He becomes a coach of how to use that technology as a tool for you, and to be aware of it, and to really wrap your head around this philosophy, which is groundbreaking in some sense.

What specifically is different, because as you said, you also did performance capture the first time around?

Last time, I had a couple of days on a motion-capture set, and most of it was done in a corner where they hide the paint on the set, with a plastic tarp on the ground, and a guy holding the camera like, ‘Make some faces when you’re smashing Loki!’ It was so low-tech and it was so on the fly, and you couldn’t marry your physical movements with your face. They could only shoot one at a time. Now they put the whole rig on you. While you’re doing the physical acting, they also capture the whole face and stuff. So you have a much more integrated performance, a much more organic performance. A performance that’s driven by the whole system.

I remember when we talked about the original Avengers, you said you discovered the key to the Hulk while watching the old Bill Bixby TV show with your kids.

[Laughs.] And he told me that he’s so misunderstood!

Yeah, that the Hulk is like a little boy, a kid who screws things up and he can’t figure out why everyone’s mad at him …

It’s all impulse. There’s no impulse control. Kids relate to him because they’re being asked to behave themselves when all inside of them, all they have is roiling emotion. And everyone around them is like, “You’re not supposed to be acting this way,” and “That’s unacceptable.’ And all they really want to do is Hulk-out. And when they see a character that actually Hulks-out, they’re like, “Yes, that’s me! I want to do that!” I totally understand.

With my kids, when they’re going off, I do the same thing Black Widow says to you in this movie: “Okay, just breathe.” If I can get them to breathe and calm down, I can get them to stop Hulking out.

And they understand. They also have their Bruce Banner version of themselves, when they’re in control, and everybody likes them. And then out comes the Hulk and everyone’s like “What’s wrong with you?”

Is the Imaginarium just like a big playroom then, where you get to Hulk-out unencumbered?

Now it gets tricky, because there’s only so much you can do at that level all the time, I think there are so many more places for him to go where he’s not always in a rage. He’s very base. He’s like pre-linguistic man. So he has all the impulses of man. It’s food, it’s survival, and it’s procreation. And so, there’s really cool, interesting places that I’m finding just by going to the gym, the Imaginarium, and I’ll just put on my gear, turn some music on, and I’ll just walk around and explore. And I found some really cool interesting stuff that I don’t think I ever would have found just walking into the character on set. Just playing, just goofing off a little bit.

So, it’s not story that helps you discover the character, but the way you move?

Yeah, it’s the way he moves. It’s really puppetry because I see it in real time. I can see my movement and how he looks when he moves, and it’s like, “Oh, I can’t move my arm like that. That’s not this image, that doesn’t feel right.” The height of him, the mass of his muscles forces you to accommodate him.

So you need to move a lot slower than is comfortable?

Yeah, it’s slower. It has more weight in it, more mass. You start to imagine, what is it like to have that kind of weight? These big, giant feet, those giant legs. Is it better straight up, or is he bent at his knees? What is his attitude towards the world? And all of a sudden, this character starts to develop and it’s all physical.

What about the other senses? Does the Imaginarium engage them, too?

Yeah, what does it sound like when you breathe, with all that mass? So they pump that through an amplifying system, and all of a sudden you have this thing. All of the available stimuli that feeds you – your hearing, your eyesight—all of a sudden it’s informing you even deeper, more clearly, more specifically into the character.

Are you drawing on any kind of animal movements?

Yeah, it started with apes, and it keeps heading back there, but there’s apes, there’s a child, there’s a coiled quality to him, like a panther, maybe? A stalking quality to him. And yeah, a lot of animals come up. The apes are good, but then he has something else. He has something else that’s even more killer than an ape.

I think people want more from the Hulk. What’s your philosophy on what Hulk would need to do to have a stand-alone movie?

I understand, but it’s a particularly hard character to make a movie about because he doesn’t want to be there, generally. It’s hard to make a movie about a guy who doesn’t want to be there. And he doesn’t want to do the very thing that you want him to do. So it gets a little frustrating as an audience, and there’s only so much of that.

I guess that’s true. The one person who doesn’t want more Hulk is Bruce Banner.

I think they set it up nicely [in Age of Ultron] that Banner’s turning 46 years old, and there comes a point where it’s like, How much more running can I do from myself? Whatever you hate about yourself or you don’t like, when you get to be 46 years old… You can never really get away from yourself, so you start to live with some things you think are so bad. And maybe they’re not that bad. Maybe those things are the very things that you need.

Where would you like to see him go storywise?

I think there’s a whole relationship with Banner and Hulk that needs to be discovered. Hulk is as afraid of Banner as Banner is afraid of Hulk. It’s in the comics. But films haven’t really been able to get inside of Hulk’s head. The technology wasn’t available to make it nuanced enough to do that, and now it is. Both of these guys—or, obviously, the same guy—have got to come to peace somehow with each other. And I think that confrontation is building along the lines of this film.

I like that. Hulk being afraid of that puny human.

He’s terrified of him

Well, that’s when he goes away.

Yes, he’s as terrified of Banner as Banner is of him. What makes Hulk afraid? It’s himself. It’s a version of himself that’s weak. It’s a version of himself that’s vulnerable. It’s a child inside of him. It’s very interesting, and I’m stumbling on this. And I don’t know if this is where the next version will go. But if it is in the cards that we’re doing the next version of this, I see some fertile ground there. I’ve been mulling this over now for a few years. And I haven’t pushed for it because I honestly didn’t know where it hadn’t already been done. There’s an interesting confrontation on the horizon between these two.

They’re fighting over the same body.

It’s existence. They’re fighting over existence, you know?

It’s Age of Ultron week at EW.com. Check back for more exclusive Q&As from the set of the new Avengers movie.

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