Dewey Cox rocks. And drinks. And does drugs. And sleeps with any number of women (and fathers a boatload of children by them).

But most of all, he rocks.

As does John C. Reilly, who plays him in "Walk Hard: The Dewey Cox Story."

It's the role of a lifetime for Reilly, who plays Cox from a teenager to an old man (older actors playing kids are a running joke). He traces the history of rock embodied in one person, from Elvis through Dylan and the Beatles to Smile-era Brian Wilson to disco and punk and beyond.

If it sounds ridiculous, well, duh.

The latest comedy from the Judd Apatow team — Apatow co-wrote the script with director Jake Kasdan — replaces the underlying sweetness of previous efforts such as "Knocked Up" and "Superbad" with a broad, out-and-out silliness.

If it's not as deep as those movies, it's often every bit as funny. Reilly in particular is fall-down-laughing funny, especially when Dewey is in all his drugged-out glory. For instance, there's an orgy scene you won't soon forget, no matter how hard you try. The audience may be shocked, but not Dewey, who at this point has seen and done so much with so many people he doesn't blink an eye.

Without giving anything away, it's a signature Apatow scene. If something's funny, he'll beat it to death, and gleefully so. The repetition, particularly with something outrageous, becomes part of the joke.

Dewey has the classic rock-star background, coddled by his mother but hated by his father for his part in a childhood tragedy, albeit a tragedy of the Monty Python variety. After discovering his talent as a musician and songwriter and finding success at a high school show, he sets out on the road with his girlfriend, where fate finds him fronting a band in a club the night record-company executives are in the audience.

In a fit of desperation in the studio, he cuts his signature hit, "Walk Hard." From there it's Rock History 101 combined with clown school, as Dewey both succeeds and falls prey to every wretched excess you can imagine. How excessive? He gets himself a monkey.

He finds love, after a fashion, with Darlene (Jenna Fischer), not letting a silly little detail like his current marriage deter him. He travels to India to mediate with the now-bickering Beatles.

All part of the swirling, mercurial life of Dewey Cox.

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