Superman kept California from tipping into the ocean, but it was Marlon Brando who made it safe for elite actors to work in comic-book movies (Gene Hackman, too, who probably deserved a supporting-actor nomination for 1978’s Superman).

These days, it’s almost expected to see Oscar winners and nominees bedeviling Batman or shooting bolts of lightning out of their hands. Even in such company, Iron Man 2’s cast is one of the best so far: Robert Downey Jr. reprising his role as Tony Stark/Iron Man; Gwyneth Paltrow; Samuel L. Jackson; the voice of Paul Bettany; Mickey Rourke; Sam Rockwell; Scarlett Johansson; and as Col. James "Rhodey" Rhodes/War Machine, Don Cheadle. The approach of a serious actor was evident as Cheadle posed what director Jon Favreau called "tough, smart questions":

"‘What are you eating? Do you think that’s really good for you?’ and ‘Don’t you think we’ve had enough doughnuts?’ " Cheadle deadpans of what he asked his director. "No, it was, ‘If this, then what? What would Rhodey feel is a betrayal to his friend as opposed to service to his country?’ "

In this sequel, opening Friday, Stark must cope with the unexpected toll life as a one-man global peacekeeping force is taking on him, while an obsessed Russian genius (Rourke) and an unscrupulous American arms dealer (Rockwell) plot his downfall. Rhodey is the strait-laced military liaison and trusted friend to Stark who, as Iron Man fans know, ends up wearing one of Stark’s armored supersuits with a somewhat-more-aggressive aesthetic. But Rhodey has to navigate the boundaries of friendship and duty to arrive at that point.

"How do we not hate Rhodey when he takes the suit? On one hand, if Tony’s not sufficiently out of control, it doesn’t make any sense why I would jump on him. But if he’s too far, you kind of don’t like Tony anymore. It was a really delicate balancing act, so the audience can at least argue about it. If half of them are saying, ‘He shouldn’t have done it,’ and the other half are going, ‘Nah, he probably needed to,’ we’ve done our job."

Cheadle, looking slender and alert in a posh hotel suite, says college friends got him into the revolutionary comics of the ’80s — Frank Miller’s The Dark Knight Returns, Alan Moore’s Watchmen and Swamp Thing — but he knew little of Iron Man ("I thought he was a robot") before Favreau approached him. After a false start with the first movie that found Terrence Howard in the role, followed by a real start with the second movie when Howard and the studio came to a contractual impasse, the star of such grown-up fare as Hotel Rwanda and Bulworth eagerly stepped in to make a movie his kids could see. Well, that, and to get into epic fights wearing a cool suit of weapon-laden armor.

"Cool is actually the opposite of what it was. It was a very hot suit. Very uncomfortable," he says, pointing out that he and Downey Jr. "did all the fighting and stuff, but you’re just a template, really. You’re the rehearsal for the action that comes later, which is the virtual. The actual is the rehearsal for the virtual."

Although much of what they did was replaced via motion capture ("The CGI version of me as War Machine and my stuntman worked as much as I did"), acting it all out was vital to the process:

"We didn’t want to have some arbitrary ‘And then they fight’ — it has to make sense with what they’re going through. The fight has to be an outcropping of Rhodey’s frustration with Tony and Tony’s inebriated, devil-may-care attitude."

It’s what isn’t obvious on the screen, though, that again marks the actor’s complex approach to a comic-book role.

"We had a lot of discussions about, ‘You can feel that way about being true to your country and the oath you’ve taken versus the unspoken oath we take to one another as friends. But what does it mean to actually take the hardware?’ He’s a fighter pilot, and the fighter pilots I’ve met — flying, that’s it for them. It’s better than anything, better than sex. Now imagine flying. You. Where does the ego come into this? Where does he want to know what it’s like for himself? Yes, it’s about protecting the country, but where’s … ‘I like it!’ That’s in there, but it doesn’t appear in the movie in any kind of overt way."

With perhaps the exception of Christopher Nolan’s Batman movies, despite big-name casts, that sort of serious character exploration is just not par for the genre (think of Tim Burton’s Batman movies). Not that Iron Man 2 becomes a heavily armed episode of Inside the Actor’s Studio — it has the humor of the original and more big, crowd-pleasing throwdowns between walking superweapons trying to reduce each other to scrap — but there was also a fair amount of improvisation in the process.

"There had to be because, when you have someone like Robert, how fertile his mind is, and I come from that kind of a background, too, theater background, finding stuff through improv. … We were given a lot of latitude to find that stuff," Cheadle says.

"The most fun was the last scene with Robert after War Machine and Iron Man do their thing. The handcuffs were off; our relationship wasn’t contentious anymore, we can go back to being friends. That was all improv. Jon would be shouting out, ‘Say this!’ All free. That stuff’s fun."

Michael Ordoña is a freelance writer.