MANCHESTER, Tenn. As Chris Rock performed in front of an audience of tens of thousands, comedian Zach Galifianakis watched admiringly offstage.

"I just thought, 'I will never be able to do this," Galifianakis joked in an interview at the recent Bonnaroo Music & Arts Festival where he performed in a smaller -- but thoroughly packed -- tent than Rock's.

Galifianakis' standup is a more intimate, ramshackle thing. His act includes one-liners accompanied by his graceful piano playing and unpredictable excursions into the audience. Thickly bearded and unkempt (he jokes that he has the body of a third-grader who's swallowed a panda), Galifianakis isn't Hollywood at all.

"Everything is just kind of like performing in my basement," said Galifianakis. "I just have this free-for-all on the stage that is hit-or-miss. . . . I kind of slam myself about that but probably the only way I can do it is just in an organized fashion somewhat. I don't really know what I'm doing."

Galifianakis may not have Rock's polish or giant fan base, but he's undoubtedly one of the most exciting comedians to emerge in the last decade. He's the prime example of a new breed of comic who rises not through comedy clubs, but whose cultish renown grows organically through performances in rock clubs and by videos circulated online.

By what Galifianakis says, though, he may throw off the spotlight just as it's brightening.

One of three children, the 38-year-old Galifianakis was born in Wilkesboro, N.C., where his father was an oil heating vendor whose vision for his sons was more football and less theater.

Galifianakis says his parents are sweet, humorous people, but he tells them his act isn't "for adults." They've only once seen him perform about nine years ago and Galifianakis purposely embarrassed them by opening with an off-color joke.

He began doing standup, he says, in the back of hamburger restaurant in Times Square. By the mid'90s, he was landing parts in sitcoms and movies.

No role has yet fully captured Galifianakis' disheveled wit, though he's been around enough to be a recognizable face: a 2002 VH1 talk show "Late World With Zach," a recurring role on the Fox drama "Tru Calling," a starring role on the fake news comedy "Dog Bites Man," a part in the Ashton Kutcher film "What Happens in Vegas," a starring role in the indie film "Visioneers," a small part in Sean Penn's "Into the Wild."

Instead, Galifianakis has distinguished himself with his standup act, which he's been more likely to perform at music venues, coffee houses and universities than comedy clubs. He was part of the "Comedians of Comedy" 2005 tour and subsequent film with Patton Oswalt, Brian Posehn and Maria Bamford.

It was then that you could see Galifianakis perform as one of his alter egos: Nathaniel Buckner, an 18th century hack comic ("Thank yee, good to be hither. . . . Is this thing on? What is this thing?")

Performing, Galifianakis is devoid of artifice. He keeps a small pad with him on stage which he frequently consults. He alternates at whim between standard joke-telling ("When you look like me, it's hard to get a table for one at Chuck E. Cheese"), strolling among the crowd and playing soft, soothing piano while he relates one-liners like "At what age do you tell a highway it was adopted?"

If anyone in the audience shouts out (a not infrequent occurrence for Galifianakis), he often exaggeratedly berates the offender and claims his "rhythm" has been thrown off.

Videos of his performances are hugely popular on YouTube and MySpace. He's perhaps most famous for his music videos, including a lip-syncing of Anita Baker's "You Bring Me Joy," a video he did with his friend Fiona Apple and one Kanye West personally commissioned as an alternate video to his "Can't Tell Me Nothin'."

For that video, Galifianakis and his friend, indie singer-songwriter Will Oldham, mocked a thug lifestyle while riding tractors through Galifianakis' North Carolina farm. (The comedian splits his time between the farm and the Williamsburg section of Brooklyn.)

His DVD "Live at the Purple Onion" has a cult following, though he says it's "selling whatever the opposite of hot cakes is."