Joss Whedon reveals Marvel's strict set of rules for handling Nick Fury in The Avengers

Marvel was not about to mess around with any of its major characters when it came to the massive superhero team-up movie The Avengers. Especially Nick Fury, says director Joss Whedon. There was zero tolerance for toying with Fury's background. Marvel drew a line in the sand about keeping the head of SHIELD's identity and intentions shrouded in complete mystery. In fact, it was the studio's strictest rule.

In a recent interview with Yahoo Whedon breaks down a lot of the behind-the-scenes secrets from the set of The Avengers — for instance how he found a happy medium with the famously improv-happy Robert Downey Jr., plus new details about Mark Ruffalo's Hulk. Here's a few of our favorite quotes:

On meshing Robert Downey Jr.'s method of working versus his own:

Well, we have very different methods. But working as a showrunner, working as a script doctor, working in sitcoms — a lot of my work has been coming up with stuff on the fly. Like fixing as we go, improvising, being open to a new idea. So Robert and I would spend — we worked specifically towards both of our processes, so that we would beat out a scene so that he was very comfortable with where it was going or what was being said and very aware of where it would fit in the whole. And I would give him stuff to say, and by and large, he would say it. But then there were always pockets where we had some wiggle room for him to play, or ask for options, and if he said, "Can we do something else here?" I could give him four or five options by the time he had his makeup on. Because that's actually fun for me, that frantic scramble. We would try different things. He is very collaborative. He loves notes. He loves to be guided and worked with. He is not trying to steamroller over me. He is really trying to create it side-by-side with me. So it ended up being a really healthy and delightful collaboration.

On finding new sides to Tony Stark:

I think the conversations were largely about "Where is Tony now?" Like, "Who is he now? Where is he [going] from 'Iron Man 2' towards 'Iron Man 3'?" He is such a well-delineated character, so it was really a question of, "What do we want to stress and what do we want to say? We have said that, we have done that, so let's not go there." He felt a sort of isolated man who is — even though there is an element of that, just because that's sort of what any team movie is about.

He didn't want to be the sort of just, "I am totally wrapped up in one thing and I am not thinking about everybody else." He didn't want to be the tortured lonely man, which I totally get. And it was easy to make him as delightful and gregarious as he can be and still go, well, there is a piece missing and it's the piece that makes him an Avenger.

On what he learned from Chris Evans' straightforward Captain America character, and how it changed him:

I love a straightforward character. I am the guy who loves Cyclops on the 'X-Men', because he is square. [Captain America] is a little square, and he is aware that he is a little square, and he is aware that the world is a beat ahead of him, or in his case, 70 beats. I think that's very disarming and very charming. I relate to that guy. I also don't know who the popular singers are right now, so he is actually really easy for me to write. There were some lines where [Chris] would be like, "Okay, now I just sound like an idiot." And in context, I was like, "Yeah, actually, now that it's all laid out that is a bit much." But he is very aware of his dignity, but at the same time understood why I wanted to find the humor in somebody who was so out of touch.

All about Mark Ruffalo and his work on the Incredible Hulk:

Yeah, he and I did the most character work of anyone, because we really were starting fresh, but we were starting with something that had been embodied several times. And both of us agreed upfront that the template for who we wanted this guy to be in his life was Bill Bixby, the TV [show character] who was busy helping other people. That was more interesting to us than the Banner in the first two movies who was always fixated on curing himself. We spent a lot of time talking about what makes us Hulk out, the nature of anger, how it feels. We even fought some. I mean literally we actually got some pads out and did some tussling. Just to talk about the physicality, and also the physicality of somebody who has to control this thing, and the way he moves in space and the way he relates to the people and the objects around him. It was extremely fun. What we found was that he could be very bumbling and kind of awkward, but at the same time very graceful and in this almost transcendent control of himself.

Working with Samuel L. Jackson as Nick Fury:

Well, he is not going to be talking about his childhood, and you do want to keep a certain mystery. Also — and this is something that I was very pleased that Marvel actually mandated — they were very interested in keeping him, not just in the sort of a mystery of how the organization operates, but a real moral gray area where you really have to decide, "Is Nick Fury the most manipulative guy in the world? Is he a good guy? Is he completely Machiavellian or is it a bit of both?" And that was really fun to tweak. I felt that in the other movies, they had been cameos and he had been called upon to come in and be Sam Jackson and bluster a little bit. And I told Sam upfront that my big agenda was to see the weight on someone who is supposed to be in control of the most powerful beings on the planet. The weight on somebody who has to run the organization and the gravity of it. Not that we don't have any fun with Nick, but he definitely — it's, I feel like a much more textured performance and at times really moving.

For even more behind-the-scenes Avengers chat check out the full interview over at Yahoo.