EXCLUSIVE: Imagine the Hollywood actor whom you’d least expect to play The Incredible Hulk in The Avengers, and maybe, just maybe, you’d come up with the name of Mark Ruffalo. He’s always been an actor’s actor and is getting critical raves in Focus Features’ The Kids Are All Right which opened last weekend. But I’ve learned that he’s now in late-stage discussions between Marvel and his brand-new agency United Talent to play this key member of The Avengers ensemble. Like Edward Norton, whom he’d be replacing, Ruffalo would bring real chops to the role. But, unlike Edward Norton, he wouldn’t an on-set asshole.

Meanwhile, let me get out of the way that Thor (May 6, 2011) and Captain America (July 22, 2011) will be in 3D. They were filmed in 2D but the plan has been for the visual effects to be rendered in 3D for Captain America while Thor will undergo more of a traditional conversion. Kevin Feige is going to great lengths to ensure this isn’t just a botched rush job. OK, enough with that.

Back to Hulk. Marvel made a pittance of an offer to Edward Norton to continue in the role. But it caught the actor by surprise that the studio decided to replace him altogether with no advance warning.

Seriously? After everything that went on in 2008 when Marvel and Norton were privately and publicly feuding over the remake of The Incredible Hulk. Eventually they settled their issues after clashing over how to cut the $150+ million pic. But what was released was Marvel’s cut of the movie, not Norton’s.

Now remember that Norton was promised big involvement and access after Marvel Studios chairman David Maisel invited the actor into the core team to rewrite Zak Penn’s script. But, in the end, Marvel ignored Norton’s ideas about how to cut the film. Even the film’s director, Louis Leterrier, joined with Norton to lobby for a longer, more detailed, more character-driven film while Marvel Studios wanted a faster, leaner one.

Sure, Norton has a difficult reputation. And he never does a lot of publicity for pics. But, basically, Marvel found him to be a pill. At the same, Marvel’s Davis Maisel acted like a jerk. I always thought that the studio would recast the role. Now they have.