In the past year, Robert Downey Jr. earned a reputation as one of Hollywood's most versatile stars, playing alcoholic, egocentric superhero Tony Stark in "Iron Man" and half-mad method actor Kirk Lazarus in "Tropic Thunder."

Now, in "The Soloist," opening today, Downey portrays a real-life person: Los Angeles Times columnist Steve Lopez, who discovers a homeless, schizophrenic musical prodigy (Jamie Foxx) and begins an unlikely friendship that changes both men's lives.

Lopez, divorced and cynical about emotional relationships, learns the value of simply showing up consistently and trying.

It's a point that Downey has learned from personal experience as he rebuilt a career derailed by repeated battles with substance abuse.

In 1993, he was an Oscar nominee for "Chaplin," a big-budget biography of screen legend Charlie Chaplin. From 1999 to 2000, he lived the role of inmate No. P50522 at a California prison. Since his release, he has been one of the hardest-working actors in the industry, finally winning a second Oscar nod last winter for "Tropic Thunder."

His personal and professional rehabilitation seemingly complete, Downey has become a star that studios build blockbusters around.

Whether the story calls for comic-book heroics, over-the-top comedy or inspiring drama, he demonstrates a shape-shifter's ability to get beneath a character's skin.

His reluctance to be pegged led him to another offbeat role for his following project, a period English mystery in which he'll star as a two-fisted, macho Sherlock Holmes.

We caught up with the ever-unpredictable actor last week by phone at his home in Los Angeles.

Q. Your dad was one of the wildest maverick directors of the 1960s indie movement, the man behind satirical cult classics like the advertising agency farce "Putney Swope." What was it like growing up around that kind of iconoclasm? How did that set you on your course?

A. It's everything, honestly. I have "Putney Swope" on my iPod. Sometimes I'll watch it and just go, "My God, what crazy stock I'm from." And what a blessing, you know?

Q. I imagine it gave you a pretty robust B.S. detector for the business you graduated into.

A. Yeah. And some of that is around-the-blockdom. You know, this is my silver anniversary of doing this, and it's really starting to get interesting.

Q. There are only a handful of actors like Johnny Depp and you who can navigate a long career and yet consistently stay fresh. What's the secret?

A. Oh, gosh. It must be my new depilatory cream. Honestly, if you stay engaged it stays engaging. There you go.

Q. In your new film, you and Foxx both play radically isolated characters. In your mind, who's "The Soloist" of the title?

A. Joe (director Joe Wright, whose last movie was "Atonement") would say he first thought it was Jamie and then realized it was me. We would all say we thought the film was about friendship and about mental illness. But we all now say the film is about faith. That's what makes things interesting. I love the theme.

Q. The film is full of reminders that homelessness could happen to anybody. Katrina could hit your town, you could fall off your bike and lose everything, you could be laid off.

A. Yeah, and hopefully once that's a foregone conclusion, can we now have empathy? In that scene with Steve and his wife (discussing life's unpredictability), I said, "I think he should start talking about the Northridge quake." Because the Northridge quake was a Los Angeles event at the time they had moved here, and had all the promise in the world of their marriage and their careers and their futures being forever entwined and beautiful. And something quite different happened. In fact, his only friend now is somebody who is a stranger to himself.

Q. In "Tropic Thunder" your character works in blackface and tells another actor how to angle for an Oscar by playing a handicapped character. So did you and Jamie Foxx discuss either of these subjects while you were working on this film?

A. (Laughs.) That film is so many shades of wrong, I love it so much. It's just so horrifically subversive and terrible. The greatest service I can do to any of my other peers of the realm, and my greatest joy, is when one of my contemporaries asks me if I will leave their outgoing message on their cell phone as Lincoln Osiris.

It's funny, you know. What 50 years ago would have been considered either good-ol'-boy entertainment or horrific racism has become razor's-edge, self-deprecating anti-Hollywood method-actor hullabaloo. It gives me so much joy. It's just the gift that keeps on giving.