Once upon a time, he was dreamy Jordan Catalano on the tragically canceled ''My So-Called Life;'' these days, he's fronting the band Thirty Seconds to Mars -- and strutting into the awards race as a transgender Texan in ''Dallas Buyers Club''

Just before taking the stage in front of nearly 7,000 fans in Camden, N.J., late last month, Jared Leto, sporting oversize dark glasses and a bulky shag overcoat, says, “I’m going to go kick some ass!” When he bounds on stage with his band, Thirty Seconds to Mars, the audience erupts, shouts along with every song, and obeys his every command. It’s hard to believe that this is the soft-spoken fellow who previously confessed, “I don’t give a flying f— about fame.”

That might sound like the typical posing of a rock star, but Leto’s résumé suggests he’s telling the truth. After a stint playing mid-’90s heartthrob Jordan Catalano on My So-Called Life, Leto sought out gritty roles in movies like Requiem for a Dream and Fight Club that smeared his pretty-boy aura. Even when he launched his band — and inspired a collective Hollywood eye roll — he refused to use his celebrity to promote it. Heck, the guy turned down a role in Clint Eastwood’s Flags of Our Fathers to tour with his band…as a warm-up act, for $250 per night. When it comes to fame, Leto takes the path of most resistance.

Yet the gambit seems to be paying off. His band is selling out arenas, and his first acting role in nearly six years has stirred talk of an Oscar nomination. In the fact-based Dallas Buyers Club (rated R, out Nov. 1), Leto plays Rayon, an HIV-positive transgender drug addict who partners with homophobic AIDS patient Ron Woodroof (Matthew McConaughey) to smuggle alternative meds into the U.S. Like McConaughey, Leto endured a dramatic weight loss for the role. And he adopted a soft, feminine Texas twang that contrasts with McConaughey’s redneck gruffness.

Leto doesn’t look like your typical supporting actor. With his radiant blue eyes and boyish complexion, the 41-year-old looks more like he belongs in Tolkien’s Rivendell. He was born in Louisiana and grew up poor, moving from state to state every couple of years with his “hippie mom” and older brother, Shannon, Thirty Seconds’ drummer. The household was a creative fun house, packed with artist friends and few rules. “Permission to shine your creative light wherever you choose came from a very young age,” says Leto, who studied painting at three East Coast art schools before heading to Hollywood in 1992. “I’m really glad that I was taught that lesson.”

He talks like this a lot. When Leto describes his music, his movies, and the videos and documentaries he directs, he sprinkles in quotes from Gandhi, Andy Warhol, and Steve Jobs. It could come off as pretentious if he weren’t so busy deflecting it. “Am I sounding too much like a self-help guru?” he asks with a smile.

When Leto is into something, he’s really into it, and his acting is no exception. He gained 65 pounds to play John Lennon’s assassin in the 2007 indie Chapter 27, and insisted on hanging out with junkies to prep for his role as a heroin addict in 2000’s Requiem. “One time he stuck a needle in his arm with water in it, just to see what it was like,” says Requiem director Darren Aronofsky. “I was screaming at him not to do that, but he wanted to go there, to feel it and understand it.”

All of that commitment took a toll, though. By the time Dallas Buyers Club landed on Leto’s desk, he hadn’t read a movie script in years. “Most of the time, these little films break your heart,” says Leto, who had also executive-produced Chapter 27. “They don’t find an audience; they don’t turn out as expected. That may have had something to do with my inclination to say no to [movies], you know?” In the meantime, Thirty Seconds had become a worldwide success. Their second album, 2005’s A Beautiful Lie, sold 1.4 million copies in the U.S., and the band has built a devoted fan base through relentless touring for largely female audiences. (Leto is single, by the way: “I’m not currently in a relationship,” he says, adding, “If I were, I’d say, ‘No comment.'”) Some of his younger fans don’t even realize that he has another career. Asked about him at the Camden show, one Philadelphia teen, Rachel, says, “Until this past week, we didn’t know that he was really into movies.”

Neither did the filmmakers of Dallas Buyers Club. When a producer first suggested Leto to play Rayon, Montreal-born director Jean-Marc Vallée (The Young Victoria) recalls saying, “Jared? Really? Isn’t he done with acting?” But Leto seduced him, literally, when the two met via Skype while the actor was on tour in Berlin. “He had a wig, he was putting on lipstick, he had a dress on, he put on some Marc Bolan music, and he was hitting on me,” Vallée says. “He was, like, giving me the eyes and saying that he loved my gray hair. He was just having fun, and I was laughing. The Skype lasted for 20 minutes, and he never got out of the f—ing character. He got the part right there.”

After landing the role, Leto lost 30 pounds in less than a month by limiting his daily intake to 400 calories. He also stayed in character until production wrapped. “I never met ‘Jared’ before the Toronto Film Festival two weeks ago,” Vallée says.

Halfway through the show in Camden, Leto apologizes to the crowd for starting late. He was delayed because he was Skype-interviewing James Franco for a new documentary short Leto’s making about the pros and cons of fame. Backstage, Leto says that he also spoke to Kanye West for the project: “He looked right into the camera and said, ‘Fame? Fame is awesome! And don’t ever let anyone tell you that it’s not.'” At this point, even Leto might have to agree.