For his role in Iron Man, Robert Downey Jr. had to audition for the first time since his Oscar-nominated performance in Chaplin.

Los angeles times / Jay L. Clendenin

To become a mega-movie star these days, a man must don the tights. With a few notable exceptions like Leonardo DiCaprio, who had the good fortune to be in the highest-grossing movie of all time (that would be Titanic), almost every $20-million man has done his time as a caped crusader, masked marvel or some popcorn equivalent, such as a pirate or extraterrestrial G-man.

Now it’s Robert Downey Jr.’s turn.

The 43-year-old ex-junkie, ex-con, Oscar-nominated professional entertainer is renouncing his title as the talent most likely to disappoint, everyone’s lovable screw-up, the walking cautionary-tale. He’s assuming the mantle of Iron Man, another in a long line of comic book renditions, which hits theaters today, kicking off the summer movie season.

Given Downey’s years as a reigning wit, an unflappable, unpredictable screen presence, the thought of him soaring the skies in a red metal suit and bopping bad guys is a little depressing to someone over 25, except for Downey seeming so darn happy about it. Really, really happy. Relieved. Maybe even grateful.

He’s about to barnstorm the world on a month-long Iron Man tour, and he’s genuinely thrilled. Finally, he’s the headliner — the one with his mug on dolls and Slurpee cups. “It’s feeling the support of the machine of the industry and all that behind you. You know, supporting what you busted your ass doing,” he explains.

Redemption

Life is finally good.

He’s not dead. He’s not on drugs. As recently as five years ago, Downey had to pay for his own insurance to even appear in a movie, and now a studio is banking a huge franchise on him, and the buzz-o-meter is off the charts. As Tony Stark, debonair super-nerd weapons tycoon turned superhero, he’s playing a character who is essentially a PG-riff on his persona — he’s decadent-lite, a self-indulgent high-flier who wakes up at age 40 and decides to do good. In the film, Stark is captured by guerrillas in Afghanistan, realizes how the arms he’s been pushing for the last decades are creating more harm than good and develops a techno-suit that allows him to fly, shoot fire and escape his jail cave. It’s an origin story, refashioned as a coming-of-middle-age saga — Stark sets out to atone for his life of sin — but will he be redeemed?

Art imitating life, anyone?

Downey’s sober re-ascension of Hollywood is a far cry from the guy who was once arrested while driving his Porsche down Sunset Boulevard naked, chucking phantom rats out the window. The years 1996 to 2000 flashed by in a blur of drug arrests and failed drug tests, capped by a year’s stint in California state prison after he violated probation. He reemerged in television’s Ally McBeal, won a Golden Globe and was fired after he tumbled off the wagon and was arrested for cocaine and methamphetamine possession.

After a year in rehab, he began rebuilding his career again, eventually nabbing more interesting movies such as Kiss Kiss Bang Bang, Good Night, and Good Luck, Zodiac and Fur: An Imaginary Portrait of Diane Arbus. Still, no one was thinking of him to top-line a would-be commercial juggernaut, and Iron Man didn’t exactly drop in his lap.

“Much to my surprise, I really didn’t fit any of the criteria for the kind of actor they thought they should cast,” Downey says.

As it turned out, he brought along his bag of amusing tricks — upgrading the character’s flip awareness — adding subtext and sizzle when there wasn’t any.

Producer Kevin Feige, who’s also president of production for Marvel, remembers being distinctly underwhelmed by the first list of potential Iron Mans sent over by the casting director. “Nothing popped for us,” he says. Director Jon Favreau, who had popularized retro-cool in Swingers, made a mainstream hit with Elf and had been brought on to give the film some hipster panache, was fiddling with something on the bookshelf when a name suddenly dropped from his lips: “Robert Downey Jr.”

“We both went, ‘That’s interesting,’ ” Feige says. They quickly dismissed the idea, but it lingered.

As it turned out, Downey wanted the part but wasn’t exactly sanguine about his chances. After he met with the Marvel team, its then chieftain Avi Arad walked him to his car and told him, “You’re a real craftsman.” It felt like one of those very kind brushoffs — Downey suspected his casting in Iron Man was unlikely.

But he didn’t give up. “Nowadays, I really, really trust synchronicity,” Downey says. “It’s not just one way. There’s a whole realm of possibilities. Everything is so connected that it’s not one single event that determines anything. I refused to not champion myself for this. I said to Jon (Favreau), ‘If you don’t mind, I’m just going to keep imagining this is possible.’ ”

“There were people in our company who directly said, ‘No. You can’t (cast Downey). Next,’ ” Feige says. They started looking at alternatives, but Favreau and Feige also set about making the case for Downey. They called the insurance companies, which had no problems with Downey anymore because he had been clean for five years. They called colleagues who vouched for him. The filmmakers pointed out that even the family-friendly giant Walt Disney had no problem putting Downey in The Shaggy Dog.

The room warmed to Downey — but still the actor would have to screen test for the part, the first time since his Oscar-nominated performance in Chaplin.

Given his spark-flying mind, it’s easy to assume that Downey ad-libs what he does on screen, quipping, prancing, dancing with effortless humor. Ironically enough, however, when auditioning for Iron Man, he prepared for the test of his life.

It’s dizzying to hear the meticulousness of Downey’s routine, but somehow the very laboriousness is what Downey seems to crave. Routine, rules, a pattern. As he talks, he drops shards of what seems to anchor him — his wife, his helpers, wing chun kung fu, a psychological commitment to the present, to not over-mythologizing what goes on in his life. That purposeful centeredness applies even to what he calls his “Red Sox experience” of landing the role in Iron Man after years of wandering in the psychological and professional desert.

“The problem was I could have gotten so stoked that I ran out of steam and wound up being sick for the two first weeks.” Now he’s learned to manage the crazy expectations of his own psyche.

“I just kind of honestly feel that this is just kind of like me making good on the promise of my late teens in a way,” he says, and he’s going to savor every second of the delayed blossoming, not just the work but the hoopla, the autographs, the machine of fame that once threatened to pulverize his soul. “Every day between now and the end of the month for me is like a kind of closure on this incredibly, ridiculously tough and wonderful and awesome and ghastly experience of coming to L.A. 25 years ago.”