Real sounds of a phony

According to John C. Reilly, star of the music-film parody “Walk Hard: The Dewey Cox Story,” opening Friday, the typical rock musician finds his sound early on in his career, then sticks to it for the rest of his life. He might make minor adjustments to keep up with the times, but his devotion to a tightly defined artistic persona never wavers.

Dewey Cox, on the other hand, knows no such stylistic loyalty. Reilly’s fictional rock-star alter ego in “Walk Hard,” Cox “totally reinvents himself every five years,” Reilly said backstage at the Roxy in West Hollywood recently before he and a five-piece band took the stage for an hourlong performance as Dewey Cox and the Hard Walkers.

That shape-shifting quality -- the ability to go from a small-town rockabilly dude to a track-suited disco maven -- is what makes Cox unique, Reilly said. “He’s kind of like the Forrest Gump of music.”

That could be it. Or maybe it’s Cox’s obsession with his nipples.

“You’ve seen the billboards,” Reilly-as-Cox bellowed halfway through the Roxy show, referring to the “Walk Hard” ads presenting Reilly in a topless rock-shaman pose a la Jim Morrison. “Now see the real thing!” And with that he ripped open his mariachi shirt and zestily caressed what the audience of chuckling industry insiders could behold only from afar.

Columbia Pictures has Reilly on the road baring his chest through tonight, when he’s scheduled to perform with the Hard Walkers at New York’s Knitting Factory. (In addition to L.A. and New York, the tour also touched down in Cleveland, Chicago, Nashville, San Francisco and Austin, Texas.)

Valerie Van Galder, the Sony division’s president of domestic marketing, says the Cox trek is part of a “Walk Hard” marketing campaign built around an emphasis on Reilly’s character. She compares it to the push behind last year’s NASCAR spoof “Talladega Nights: The Ballad of Ricky Bobby,” in which the film’s star, Will Ferrell, made the racing-event rounds as his character.

“We’re trying to do fun, clever things about Dewey Cox’s place as a rock ‘n’ roll legend,” Van Galder says. Among them: a series of VH1 and YouTube spots featuring real-life rock stars such as Sheryl Crow and John Mayer discussing Cox’s influence, as well as the so-called Cox Box, a lavish promotional set housing items that include a piece on the mock rocker’s life and times by Rolling Stone writer and editor David Wild.

Producer Judd Apatow, who also wrote the script with director Jake Kasdan, says that focusing so heavily on the Cox character wouldn’t work if Reilly weren’t so invested in the role.

“John was involved in every recording session we did for the songs in the movie,” Apatow says. “He didn’t just come in at the end and sing. When a song would come in in demo form, he’d sit and talk about how to approach it, just like any band. It’s rare to find someone with that much interest.”

At the Roxy, Reilly succeeded in demonstrating that, though Cox is a product of make-believe, his talent as a singer is not. An experienced musical-theater veteran who believes “a great song is like a great monologue,” Reilly expertly channeled rock ‘n’ roll greats such as Buddy Holly, Brian Wilson, Bob Dylan and Johnny Cash, whose “Ring of Fire” got the flattery-by-imitation treatment in opener “Guilty as Charged.”

One of “Walk Hard’s” most appealing qualities -- and one that Apatow says was among his primary goals for the film -- is the way it takes the air out of the overinflated self-regard that courses through many music biopics. The movie opens, for example, with Cox’s drummer telling an antsy production assistant on an award-show set that Cox can’t be hurried, as he has to ponder his entire existence before he can play a single song.

Reilly repeatedly tapped into that gleeful iconoclasm onstage at the Roxy, most memorably when introducing “Beautiful Ride,” Cox’s latter-day account of misadventures on and off the road. “I wrote this song near the end of my life,” Reilly deadpanned. “It’s a difficult period to remember.”

Despite the film’s bounty of music-nerd trivia, “you don’t have to have seen ‘Ray’ and ‘Walk the Line’ to understand what we’re doing, because we’re not just redoing something you’ve already seen,” says Jenna Fischer, who portrays Dewey’s wife, Darlene. “We’re actually creating very real characters. We play this movie totally straight. When Darlene’s begging Dewey to get off drugs, we’re really crying.”

Adds Kasdan: “You can do absurd scenes and still have the audience invest in them emotionally. It’s totally ridiculous, but it works because [Reilly and Fischer] both have this level of commitment to the truth.”

Van Galder dismisses the idea that “Walk Hard” might have trouble selling baby-boomer memories of the 1960s to the younger audience Apatow has cultivated this year with “Knocked Up” and “Superbad.”

“I see the movie as a comedy,” she says. “It’s funny even if you don’t get every reference. For older people, the music stuff is another top note.”

For Reilly, Dewey Cox is one character he’d be happy playing even without a movie to do it in. Asked whether his tour as Cox might continue after the film’s release date, Reilly said, “If they love [him], I’ll deliver.”