He rocks. He takes roles. But how did 'High Fidelity' highlight Jack Black become a leading man in 'Shallow Hal'?

Last night, Jack Black was a monster of rock.

As the lead singer of the comic acoustic-metal duo Tenacious D, Black sauntered on stage at L.A.’s Wiltern Theatre with partner-in-crime Kyle Gass; each was clad in a black high-priest robe. After crew members ceremoniously removed the guys’ threads, the self-proclaimed ”Greatest Band on Earth” strapped on their guitars and unleashed two sweaty hours of twisted tunes (such as ”Kielbasa” and ”F — – Her Gently”) on the crowd of 2,200 D-sciples.

”I think the children were moved tonight,” Black confided during the after-show fete. ”But I wasn’t really enjoying myself. I was very stressed because my mom was in the audience and I feel really dirty and wrong when she’s there…. The peeps seemed to enjoy the show, though, so I should just stop my complaining and party.”

Indeed, there’s much to celebrate. The D, who tasted cult success in a 1999 HBO comedy series, are now inciting a modest mainstream mania, selling out tour dates across the country and entering the Billboard chart at No. 33 with their self-titled debut album. Still, Black isn’t even thinking about quitting his day job: The 32-year-old UCLA dropout-turned-character actor is also the star of Shallow Hal, the new Farrelly brothers comedy about a looks-obsessed schmo who falls for an obese woman whom he sees as a skinny hottie (Gwyneth Paltrow). After a decade of relatively minor celebrity — his film resume begins with 1992’s Bob Roberts and is punctuated by a scene-swiping turn as a high-strung record clerk in last year’s High Fidelity — Black is finally getting the chance to bring his wham-bam-and-a-side-of-ham comedy front and center. And if you don’t know Jack, Gwyneth Paltrow, for one, thinks it’s time you did. ”I worship him,” she raves. ”He’s beyond brilliant. He’s like the most charismatic guy and he’s completely sexy and funny. His secret weaponry is too good to keep a secret.” Wanting to experience some Black magic up close, EW sat down with the actor (who next costars in the ensemble comedy Orange County) to chew the fat about his latest project.

EW Why did you pick Shallow Hal for your first starring role?

BLACK Because it was a no-brainer. No one else would be offering me the romantic lead. It’s not really something that I pursued, but when it was offered, it was so flattering and weird, I was like, ”Well, this is the only chance I’m ever going to get to do that. And it’s opposite f — -in’ Gwyneth Paltrow?” I may not be good, it may be a train wreck, but you’ve got the Farrelly brothers and Gwyneth Paltrow.

EW How’d you hook up with the Farrellys? Were they fans of High Fidelity and the D?

BLACK They’d heard about the D, but they were High Fidelity fans. They loved that movie and they talked with the director, Stephen Frears, a couple times. This movie had been floating around in their camp for a while, this Shallow Hal deal. And Peter [Farrelly] actually said he was thinking about playing Hal. But then he thought, ”This isn’t a little art movie where I can just be the lead.”