After three decades of dramatic ups and downs (both on-screen and off), Robert Downey Jr. is now appearing in arguably his most commercial role ever as the brilliant, self-absorbed businessman Tony Stark in Marvel’s Iron Man. “I dare anyone to find a movie where there is more heart,” Downey Jr. tells Tara Bennett.

It looks like you had a hell of a time playing Tony Stark.

Yeah. I mean come on…To see something that really works and people respond to favourably and to be the guy in that – I still don’t quite get it.

Do you like playing Tony Stark because he doesn’t turn into a Superman-style superhero?

Sure. He just starts off as a guy who is desperate to save his own life and he’s very surprised when he is put into a position where he has to do so. I don’t think he had a sheltered life. I think he was in a lot of denial about the ramifications of what he did for a living. I don’t think it’s a film about someone’s conscience getting the better of him. I think it’s a film about survival and being conflicted.

I think it’s a pretty apt metaphor for the 21st century and human beings. We have such a wealth of information, yet 20 years ago you couldn’t just go online and say, “Well that’s my opinion.” You tended to go out and do something about it or even write a letter about it. I just love that kind of action - of someone that is sheltered by choice and then takes action.

The whole film is about heart. It’s subtly about heart. I got it…everyday when they were gluing an RT to my chest. It’s the heart centre and I read a lot of Bodhi Tree bullshit and now I literally have it glued to my heart. I dare anyone to find a movie where there is more heart.

How was it collaborating with Jon Favreau?

Well, Tony Stark is Jon Favreau. His direction and my execution - and sometimes my ideas and then his direction of those ideas…Sometimes we wrote something together on paper and said, “This is not going to work!” And then we shot and it really worked. We were so lucky and fortunate every day…and at then end of the day, if we were less happy we’d give it another shot.

What makes Tony stand out from the comic book pack?

Again, going back to the obvious metaphor that his wound or weakness ultimately winds up being the source of his strength. I guess that’s why Stan Lee said he created this character on a dare - to see if, in the very anti-establishment late 60s, he could make a Howard Hughes-esque billionaire weapons manufacturer in a very non-military oriented society and let him have this wound. He said they got more fan mail than they got for any other character, particularly from women who felt they could turn Tony around.

How was it working on a project like this with such a high calibre cast?

Gwyneth’s [Paltrow] instincts were really, really sound and Jon’s and mine tended to be not far off on any given day. If we weren’t sure, we’d check in with her.

Terrence [Howard] is so smart and has such a knack for dialogue and ideas...We were really concerned about Tony and Rhodey’s relationship. There are so many relationships that we were juggling. You’ll see we go through a series of events together - such as him coming on my massive private plane to go to this weapons test or my rescue and escape - that are really good scenes by any movie standards, even if it wasn’t an action movie. Some of it is really touching and remarkably funny and offbeat and pushes the limits. That was all stuff we created.

Jeff Bridges [Obadiah Stane] is the old-school master. During the time we were shooting, I said to my son, “Are you ready to see The Dude?” (Laughs) We brought on The Big Lebowski and he was like, “That was awesome!”

Iron Man opens in UK and US cinemas in 1 May 2008.