Hollywood has long loved the musical biopic: Ray, Walk the Line, The Buddy Holly Story, Words & Music, The Glenn Miller Story. ... So it was never a question of when someone would get around to spoofing it. It was just a question of who.

Fortunately for us, it was Jake Kasdan (Orange County) and Judd Apatow (Knocked Up, The 40 Year Old Virgin). And fortunately for us they stocked it -- it being Walk Hard: The Dewey Cox Story -- with a wonderful cast: John C. Reilly, the man who nearly stole Talladega Nights out from under Will Ferrell, as Johnny Cash parody Dewey Cox; Jenna Fischer (Pam Beesly in The Office) as his very own June Carter, Darlene Madison; and Harold Ramis of Ghostbusters fame as one of the Jewish agents who discover Dewey at a black nightclub where he's filling in for the venue's broken-down star.

But we get ahead of ourselves. First, as in any good musical biopic, we have to flash back to the star's humble beginnings and find the thing that makes him (or her) tick -- like a time bomb, of course.

In Dewey's case it was a little matter of him cutting his brother in half with a machete while they were playing in the family barn one day -- an accident made all the more melodramatic by the fact that Nate Cox (Chip Hormess) was, at age 12, already an accomplished classical pianist and the one true love of Pa Cox (Raymond J. Barry).

So how does any self-respecting musician make up for the fact that he killed his brother -- being driven "smell-blind" in the process -- and enraged his father? By leaving home at age 14 with his girlfriend of 12, of course, and working his way through a biopic compendium of cliches that only seems to grow longer with each passing decade.

It begins, naturally, with a Buddy Holly-like ballad, "Take My Hand," that causes a riot -- complete with scythes -- at the Springberry (Ala.) High School Talent Show. It quickly rolls over into risque rhythm & blues as Dewey, who's working as a janitor in a black nightclub, performs "You've Got to Love Your Negro Man" (co-written by Reilly) for an all-black audience, then goes country with "Walk Hard," a song that comes to him as his wife and the mother of his first five children walks out on him.

Dewey even morphs into monochrome for a Dylanesque patch in the early '60s before meeting the Beatles (Jack Black, Justin Long, Paul Rudd and Jason Schwartzman) and turning, with a little help from his new friends, into an animated character -- then doing a Partridge Family-like tour, complete with a bus and a large number of his 23 or so children and 14 or so stepchildren.

But to dwell too much on the story is to miss half the fun of Walk Hard, which plays out best in the film's absurd dialogue, from the doctor's diagnosis of Nate's accident -- "This was a particularly bad case of somebody being cut in half" -- to Dewey's boss in the nightclub (Paul Bates) yelling at him to stop trying to be a singer and start cleaning up: "My customers come here to dance erotically," he says, "and they need a clean floor to do it on."

Still, what would a musical biopic be without some memorable songs, and Walk Hard has lots of them, from the title track, which provides background for a musical montage corny enough to be in the world's worst rockumentary, to the extremely edgy "Let's Duet," in which Reilly, who does his own vocals throughout, and Fischer spar, Carter-Cash-like, before a live audience with lines like "In my dream you're blowin' me ... some kisses" and "You and I could go down ... in history."

Finally, big kudos have to go to cinematographer Uta Briesewitz for putting the perfect biopic glow on every daytime scene and the gratuitous gloom on every trip Dewey makes to the men's room, whether it be to tear the sink off the wall (a running gag that just keeps getting better) or take some drugs with his band mates.

The result is that Walk Hard looks like a biopic, sounds like a biopic, acts like a biopic and works like a biopic. But it goes biopics one better: It puts them in their place. It's the pick of the biopics, musical or not. Dewey Cox rocks.