After playing numerous sad sacks, John C. Reilly is finally getting his chance to be a superstar -- or at least a fake one. Directed by Jake Kasdan, Walk Hard: The Dewey Cox Story features the Chicago native as the titular Zelig-like singer, who overcomes a troubled childhood to become a music icon, inventing punk and dropping acid with the Beatles along the way. "He's a shape-shifter," Reilly, 42, says of Cox. "He's a brilliant, tormented genius." Walk Hard perfectly mocks the conventions of the rock biopic, down to the weepy closing ballad. "We're making fun of the formula," Reilly says, "but we're also using the formula."

Obviously, Walk Hard is a comedy, but it also feels like a critique of the biopic genre.

If anything, the smart-ass part of us is trying to say, "Isn't it time to be a bit more honest about these complicated lives?" Because if you are obsessed with Johnny Cash or Ray Charles, when you see [their lives] shoved into 90 minutes, you can't help but feel a little gypped. On one level, all biopics are a bit of a letdown.

What about them rings false?

That the not-so-positive aspects of peoples' lives are touched on so briefly; like, [assumes narrator's voice] "Ray Charles dabbled in heroin -- moving on! Then he wrote 'What'd I Say.' " When we showed Walk Hard to audiences the first time, the dark periods were much longer. But as funny as we thought it was for me to have sex with ten women in a row, after a while, I think the audience didn't agree. They want the person to be a hero.

Now that you've played a musician who goes off the rails, do you see why they go crazy sometimes?

Somebody said, "Fame allows you to become the asshole that you could be." When you have a hit song, boom! You're shot out of a cannon and the money just comes pouring in. If you're a famous musician who's surrounded by people being paid to keep you happy, you don't have those grounding influences anymore, and that's why people go bananas.

When Dewey has his first hit, he goes a little bananas: He buys a giraffe and an ape.

Yeah, and a camel -- all kinds of shit! [Laughs] We're playing with some famous stories there. I actually pushed to have a chimp in the movie because Elvis had this chimp named Scatter. Elvis would ignore people, and he would only talk to Scatter. That really says something about the rock star's life, when the only person you trust, the only person you'll talk to, is a chimpanzee.

In the movie, after you smoke weed for the first time, you get naked and have an orgy.

Well, it's a gateway drug, you know.

What did you do the first time you smoked weed?

Oh, I'm going to plead the Fifth on that one.