Robert Downey Jr - High on another kind of hit now

'Last time we saw him as this hapless, charming prick," teases the ever-confident and self-assured Robert Downey Jr, grinning at the unspoken implication that he could just as easily be describing himself, rather than his on-screen alter-ego, Tony Stark or Iron Man.

For Downey has every reason to feel smug, having turned his career around from the depths of drug addiction, when few studios would even take a chance on him. He conquered his demons to become one of the most bankable actors in Hollywood, at the same time settling into a happy marriage with the successful film producer Susan Levin.

Sashaying into a San Diego hotel room, resplendent in a lilac pork-pie hat, violet T-shirt, skinny jeans and jewel-encrusted necklace, he tantalisingly thrusts a black rubber brief-case on the table. One has to ask...

"Ha! It's the same garbage as always. My routine hasn't switched up for a while," he smiles, opening up his case and rustling through assorted bottles and sprays. "Dandelion root, sunglasses, vitamins to keep the germs at bay, and, umm, don't know what this is...?" he says, scrutinising a bottle of prescription pills.

He says this with the unshakeable confidence of a cleaned-up, two-time Oscar nominee who is back on top of his game. The box-office successes of Iron Man and Sherlock Holmes have effectively dispensed with the "I kicked drugs and now I'm back" headlines of yesteryear. Today, he's invincible – a little like Tony Stark, beneath whose iron armour he was catapulted back to glory, Hollywood opening its cheque-book in his fearsome wake. Putting his junkie days firmly behind him, Downey Jr now has an even more compelling addiction: to power, glory and fame.

Driven to make up for a lost decade, he did just that with Iron Man, seizing his new-found bankability with both hands. At 45 years old, he has clearly become comfortable with re-joining the establishment, a task made all the easier by his marriage in 2005 to Levin, who worked with the formidable uber-producer Joel Silver at Silver Pictures.

With his wife serving as executive producer on Iron Man and his long-time friend Jon Favreau as director, it's clear Downey's involvement in the film extends far beyond being its passive star. He discusses casting and character development like a veritable corporate executive, earnestly defending the choice of Mickey Rourke as his nemesis in this high-stakes sequel. "We fought for Mickey to be in our film but then he fought for us because his people were, understandably, like, 'Hey! He's a really big deal right now, and we want to make sure that he's gonna be properly serviced.' And Mickey made some really great choices, which is why we hired him as 'bad guy' Ivan Vanko because we figured he would."

But Downey finds it impossible to remain serious for too long, mischievously poking fun at his co-star, whose devotion to Method acting resulted in him spending time in a Russian jail prior to filming: "How bad-ass was Mickey with those whips?" he grins. "But, really, at the end of the day, its just two schmucks in trailers and once in a while I'd be like, 'Hey, mind if I used your treadmill?' And Mickey goes, 'Yeah, you should try my weight vest. Helps you break the sweat quicker.' And I'd be, 'OK. See you on set, bad guy', and he'd say, 'OK, punk.'

"I'm not fully a Method guy but I like playing around with that energy sometimes. And Mickey wanted to do his part in Russian; he had a dialect coach who taught him and translated, so that was a very unique take. From the very start, he said, 'I don't want it to be Dolph Lundgren from Rocky V. I want to bring humanity and dimensions into it.' And I think he did that."

Thus invested in the success of Iron Man 2, Downey Jr says: "We felt more responsible to spend more time broadening our cast and horizons, and the story is actually significantly more complex and subtle, while you can still follow it." He is re-joined in the sequel by Gwyneth Paltrow as Pepper Potts and Samuel L Jackson as Nick Fury; newcomers to the series include Scarlett Johansson as Black Widow, Sam Rockwell as Justin Hammer and Don Cheadle as Col James Rhodes, the latter replacing Terrence Howard in the role.

As Iron Man became one of the highest-grossing movies of 2008, it totally changed Downey's public profile. "It's pretty miraculous," he concedes. "Although I'm not sure the public's opinion of me changed, it was more of a movie industry thing. Nonetheless, it's mind-blowing to me because I'd always felt like I could do something like this when nobody else agreed. It's wild. But I do try to keep my confidence in check. I think the thing that's been my saving grace, is that I consider myself a worker among workers. When I deviate from that, things just don't turn out so sweet for me. Now, because I'm married to a producer, I'm also kinda being given an education into what it's like to manage a bunch of creeps like me, and what it actually takes to get something done and schedules and budgets and all that kind of stuff."

Having dated Sarah Jessica Parker for several years in the 1980s, Downey married the actress Deborah Falconer in 1992; the couple had a son, Indio, who is now 16. Only with Levin, however – who he met when she produced his 2003 film Gothika, and married two years later – has he found the stability he needed in life. "I don't joke when I say she is my better half. She truly is. I cannot believe what a fantastic life I have today. But here's the thing, she didn't change me at all. She just gave me an ultimatum at a certain point. Ultimately, we both changed a lot so that now I can't ever imagine a life before her. I've certainly come to believe that Mrs Downey and I together are definitely better than me alone or me and anybody else. We love working together. It's hard not to work together and, believe me, I know my place. Making movies is so energy- and time-consuming that it takes you away from your real life for big chunks of time and, so, I get to escape with her as opposed to from her."

If life on Planet Downey is generally fabulous, he can't resist a small whine: "The suit was a little easier this time round although not enough for my taste. I was physically in the suit twice as much this time as last time. Despite being put under the impression that with the advances of CGI since I last wore the thing, it would be three or four days max in the suit, it turned out to be much, much more. Also, I just got older, and I came off Sherlock Holmes, where I was alarmingly thin and then proceeded to start pumping up again."

The son of the underground film-maker Robert Downey Sr, Downey Jr made his film debut at the age of five as a puppy in his father's film Pound, later claiming that his own father introduced him to drugs, offering him a marijuana joint when he was eight years old. Early successes came with Weird Science and Less Than Zero, before he achieved critical acclaim with Chaplin, earning an Oscar nomination and a Bafta award in 1992.

Thus followed an eclectic career, with disparate roles in Natural Born Killers, Richard III and Restoration. Spiralling into drug addiction during the late 1990s, and spending several months in jail from 1999 to 2000 on charges of probation violations, he still managed to pull off convincing performances in The Gingerbread Man, Bowfinger and Wonder Boys. Post rehab, he cemented his comeback with Kiss Kiss Bang Bang, Good Night, and Good Luck and Zodiac, followed by a second Oscar nomination in 2008 for Tropic Thunder.

Today, he is looking to mix things up. Later this year, he will appear in road trip comedy Due Date. He's also rumoured to be playing the writer Edgar Allan Poe in Poe, a film treatment written and due to be directed by Sylvester Stallone. Optimistically attached to a third Iron Man in 2012, Downey is also signed up for The Avengers the same year: Ask whether he ever envisaged himself as the hero of a multi-million-dollar comic-book superhero franchise such as Iron Man, he quips: "Yeah. I imagined myself playing one every year. They just never gave me the part."

'Iron Man 2' opens on 30 April