Zach Galifianakis is the man-boy comic of the moment

In the first few minutes of "Due Date," which opens Nov. 5, a cranky architect played by Robert Downey Jr. spots a strange man at the Atlanta airport.

The wild hair and thick orange beard are disturbing enough, but it's the weirdly preening walk and unacceptable scarf that cause Downey's nose to wrinkle instinctively. Nevertheless, the chubby-cheeked fellow returns a sunny smile, the kind that says: "Let's be friends!"

This is Zach Galifianakis, whose burgeoning career is built on playing the grown-up version of the weird kid you avoided in grade school, the one who invaded your space, talked about bodily functions and instantly drove away your cool pals and every cute girl in sight. Galifianakis excels at this role, whether as a friend of the bridegroom in last year's hit "The Hangover" or as a comics-drawing stoner in the HBO series "Bored to Death." That Galifianakis also manages to find the soft, sensitive center of that character is part of his appeal.

"I have a lot of growing up to do," goes one of Galifianakis' early stand-up lines. "I realized that the other day, inside my fort."

Sandler, Ferrell, Rogen . . .

That fort has long been crowded with man-boy comedians. Adam Sandler ruled the roost during the 1990s, throwing tantrums in "Billy Madison" and "Happy Gilmore." He was deposed by Will Ferrell, whose persona - basically, a 6-year-old with body hair - hasn't changed much since 2003's "Elf." In the late 2000s Seth Rogen took over, playing an overgrown adolescent in "Knocked Up" and "Pineapple Express." (Danny McBride, the blustery star of "The Foot Fist Way" and HBO's " Eastbound & Down," is hovering on the periphery.)

Is it Galifianakis' turn? At 41 he is decidedly old for a new comedian, but his appeal skews young. He practices a style of cerebral, absurdist, culturally savvy comedy that's been hip with college kids for decades, from Monty Python and National Lampoon to David Letterman and Cartoon Network. Galifianakis values the awkward pause and the non sequitur above the traditional joke. He also tends to get self-referential, commenting on the conventions of stand-up comedy itself: "Usually I'm supposed to end pretty good. But that's so '90s."

During the mid-2000s Galifianakis built a following on the traditional comedy club circuit, but it was the anything-goes Internet that turned him into a dorm-room, if not a household, name. In 2006, he starred in Fiona Apple's video for "Not About Love" (he played the world's most irritating boyfriend) and later accepted Kanye West's offer to direct a video for the single "Can't Tell Me Nothing" (it featured Galifianakis and the singer Will Oldham goofing around on a tractor). He also helped create a series of slapdash short films - for Absolut vodka, oddly enough - that gave him more traction than any brick wall and spotlight ever did.

To this day, Galifianakis maintains an Internet presence. On the comedy site funnyordie.com, he hosts a talk-show spoof called "Between Two Ferns With Zach Galifianakis," where he has hectored and insulted such luminaries as Ben Stiller, Jon Hamm of "Mad Men" and Natalie Portman (his opening question to her: "What is your phone number?"). Recently, though, his fake show has begun to resemble a real one, pulling in actors who happen to be starring in his movies, like Steve Carell of "Dinner for Schmucks" and Bradley Cooper of "The Hangover."

He's a player

It's one small sign that Galifianakis - a somewhat reclusive figure who doesn't retain a personal publicist and lives on a farm in his native North Carolina - is becoming an industry player. In a recent interview on the podcast "Comedy Death-Ray," he even struck the pose of the aggrieved Hollywood thespian: "But a movie you're acting in, you don't have a lot of control. You just show up and vomit your lines out. I'm not the boss. I'm in a deep protest right now with a movie I'm working on, up in arms about something." The host, Scott Aukerman, seemed to assume they were talking about "The Hangover 2," but before he could utter the title Galifianakis cut him off. "I'll tell you about it later," he said. "It's very frustrating."

This comes on the heels of Galifianakis' dramatic turn as an emotionally fragile psychiatric patient in "It's Kind of a Funny Story," written and directed by the indie darlings Anna Boden and Ryan Fleck. It was the one role, Galifianakis has said, for which he did research; after visiting psychiatric hospitals, he tried to re-create the wan expressions and red-rimmed eyes of the people he observed. The film, released earlier this month, earned middling-to-good reviews, and critics seemed impressed by Galifianakis, who added a layer of middle-aged dysfunction to his usual childlike persona.

Which brings up the question: What does Galifianakis do next? At some point, most comedic actors long to become serious ones, though few succeed. Jerry Lewis never quite managed it; Robin Williams and Bill Murray did. Woody Allen and Steve Martin became credible dramatic writers, though dramatic roles have generally eluded them. Sandler wowed critics in 2002 as the star of Paul Thomas Anderson's "Punch Drunk Love" but soon returned to broad comedies like "Anger Management." Ferrell, in 2006's metaphysical drama "Stranger than Fiction," barely registered.

The tagline for Galifianakis' road-trip comedy "Due Date" is "Leave Your Comfort Zone," though it clearly doesn't apply to the actor. For now, Galifianakis seems to be deciding how far to venture outside his fort.