As an actor, John C. Reilly is the opposite of Mr. Cellophane. He doesn’t disappear into a role; roles disappear onto him — the unlikely porn sidekick of Boogie Nights, the inadequately adequate family man of The Hours, the cutup cowboy of A Prairie Home Companion, all stamped and imprinted with the actor’s doughy kisser. The only catch is, the role has to exist first. He’s a character actor in the true sense: He’ll provide the perfect coat rack, but someone’s got to hand him a coat.

As Dewey Cox, a hard-livin’, hard-lovin’, hard-everythingin’ singer with a Zelig-like proximity to every major music figure of the past 50 years, Reilly cuts a hilarious and electrifying figure — live. On a recent promo tour, playing Nashville’s Mercy Lounge in a concert that was part Spinal Tap, part Hedwig and the Angry Inch, and completely riotous, Reilly slipped hungrily into the guise of a surly, self-obsessed spotlight hog. Surprisingly lithe and snake-hipped, he played selections from his protest-singer phase (“not that I believed in that shit”), bestowed female patrons with hankies steeped in ball sweat, and congratulated the crowd for its taste: “I’ve never heard so many men say, ‘I love Cox!’?” His Dewey was an arrogant bastard — and more important, he was funny as hell.

Sadly, Walk Hard: The Dewey Cox Story isn’t. And seeing Reilly perform the material live only points out how fundamentally misconceived this barrage of dry-docked yacht-rock gags is at every level — starting with its flaccid Cox. (Live by the dick joke, die by the dick joke.) It’s not that the pop biopic isn’t ossified enough to get its own Epic/Date/Scary Movie: There were moments, watching La Vie en Rose and Ray, when you could swear it already had. You better walk the line, Johnny Cash! Hit the road, Ray Charles! Vous ne regrettez rien, Edith Piaf! But this burlesque of biopic clichés founders from one setup to the next without the engine that drives the genre: a strong central character.

Scripted by the high-powered team of Judd Apatow and Jake Kasdan and directed by Kasdan (who made the wonderful Zero Effect), Walk Hard often plays like a scene-for-scene nose thumbing of Walk the Line. Only Dewey is less a Man in Black than a twerp in twill: a humble country boy who steps forward at his high school talent show to croon a mushy ballad. This being a pop biopic, it takes all of a stanza to induce a riot, prompt cries of “It’s the devil’s music!” and unleash an epidemic of teenage lust. It also bum-rushes Dewey down the path to stardom, leading to an affair with dewy duet partner Darlene (Jenna Fischer, in a Reese Witherspoon parody that’s one joke shy of a one-joke part) as well as busted marriages, drug addiction, patricide — and, at rock bottom, his own ’70s variety show.

Reilly’s Roy Orbison–ish tenor is game for anything from funk to punk, and he’s been given a ready-made hit parade of clever knockoffs (by Dan Bern, Marshall Crenshaw, Mike Viola, and more) — though the brilliant “Dear Mr. President” (“I’m deeper than you”) is inexplicably relegated to the soundtrack album. Had Dewey been the mean, obscene sex machine of Reilly’s live shows, Walk Hard might’ve been a hoot — at least as funny as the recent Will Ferrell comedies it resembles, down to the unnecessary attempt to make the self-infatuated hero ultimately lovable.

But Dewey doesn’t hang together as a character. He’s a blank festooned with ill-fitting traits swiped from a season’s worth of Behind the Music episodes, and when the movie isn’t sending up something specific — Cash’s drug habit, Dylan’s protest singing, Brian Wilson’s obsessive mania — Reilly has nothing to play. (Maybe this is the movie that should’ve been called I’m Not There.) Gag-a-minute Airplane!-style comedy isn’t Apatow or Kasdan’s strong suit, either. Even when the skewering of biotropes is spot-on — as in the obligatory conquering-the-charts montage for a single “recorded just 35 minutes ago!” — the timing is off, stifled by Kasdan’s needlessly glossy direction or Apatow’s ability to flog a running joke into whimpering exhaustion. “The wrong son died!” barks Dewey’s dad, still raw over the accidental machete-halving of Dewey’s brother: Not even an actor of Raymond J. Barry’s gifts can make it amusing, the first time or the dozenth. (For one thing, even if comedy equals tragedy plus time, there’s still something distasteful about parodying the all-too-real death of Johnny Cash’s brother.)

The biggest laughs come from players who know how to hit their sketch-comedy marks quickly and move on: from Tim Meadows as Dewey’s drummer, whose antidrug warnings inevitably turn into a can’t-resist/come-hither, to Harold Ramis as Mad magazine’s idea of a Jewish record mogul, more likely to cut foreskins than 45s. The rest of the movie blows through opportunities like Motley Crue through coke money. It takes almost a perverse determination to put Jack Black, Paul Rudd, Jason Schwartzman and Justin Long in a room together as the Beatles, then give them so little to do that even Eddie Vedder’s cameo as an awards-show presenter smokes them. (The DVD extras will almost certainly be better.) Walk Hard limps soft — but if John C. Reilly turns up anywhere onstage in your town, go. If there’s anything America needs now, it’s more Cox.

WALK HARD: THE DEWEY COX STORY | Directed by JAKE KASDAN | Written by JUDD APATOW and KASDAN | Produced by APATOW, KASDAN and CLAYTON TOWNSEND | Released by Columbia Pictures | Citywide

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