LOS ANGELES – How do you discover your inner goofball?

For Will Ferrell, the eureka moment came relatively late, years after the other boys had learned the joys of disrupting class. He was a high school senior, a conscientious student and a jock (basketball captain, baseball player, kicker on the football team), much too popular and well adjusted to crave class-clown validation. But then a friend asked him and a buddy to work up some shtick for the morning P.A. announcements to help sell Class of ’85 T-shirts.

“They were like old radio skits,” recalls Ferrell, brightening at the memory. “We’d do voices, like the old Irish Spring commercials.” Here Ferrell adopts an Irish brogue: ‘You smell like a bucket of vomit. Why don’t you wear this – your senior-class T-shirt!’ ”

Ferrell loved it. More important, the other kids loved it. Even the teachers at University High in Irvine, Calif., in the heart of Orange County, started egging him on. Ferrell started staying up late to write more bits, skipping his homework. He and his friend started performing sketches from “SCTV” at school assemblies. More hilarity, more praise ensued.

You already know where this leads. A few years later, post-college, Ferrell has become a member of the Groundlings improv group in L.A. He gets a tryout with Lorne Michaels and “Saturday Night Live” – and kills. About 6,000 distinctive Ferrell characters and bits follow: Harry Caray, Craig the Cheerleader, James Lipton, Alex Trebek, George W. Bush, More Cowbell. With his “SNL” co-writer (and now collaborator/business partner) Adam McKay, Ferrell goes on to make movies, including their absurdist masterpiece, “Anchorman: The Legend of Ron Burgundy.” They also write a Tony-nominated Broadway show with Ferrell as Bush, “You’re Welcome, America,” and start a comedy website, Funny or Die. Which kills, too, thanks notably to “The Landlord,” a short video starring Ferrell and McKay’s 2-year-old daughter, Pearl.

Not incidentally, it all leads to Ferrell’s selection as the recipient of the 2011 Mark Twain Prize for American Humor. The Kennedy Center handed the award to Ferrell in one of those made-for-TV gala-specials (it will air on PBS stations tonight), putting Ferrell’s name alongside such former winners and comedy legends as Richard Pryor, Bill Cosby, George Carlin, Neil Simon and Carl Reiner. Pretty sweet. Or as Ferrell-as-Lipton might say, “Scrumtrulescent!”

At 44, Ferrell’s still on the young side to be joining comedy’s Hall of Elders (on the other hand, Tina Fey, Ferrell’s former “SNL” running mate, was just 40 when she received the same honor last year). But it’s hard to dispute Ferrell’s gifts as a comic actor and writer.

On this day in mid-October, Ferrell seems as sunny and mellow as the 90-degree heat warming Southern California. He’s unshaven, and pads around his office, a restored 1920s-era building off Melrose Avenue, in cargo shorts, Adidas and a USC T-shirt, which is approximately the same attire of the young staff bouncing around the corridors.

Ferrell and McKay decided to call their company Gary Sanchez Productions, which they tell visitors was the name of their mutual hero, a legendary Paraguayan placekicker who played for the Vikings and Chiefs in the NFL. It’s a goof – they just made the name up – but both men were delighted when a Hollywood trade paper printed their bogus story straight up.

The antic spirit born in Ferrell’s senior year of high school was nurtured at USC, a school probably better known for incubating tailbacks than comedy stars. Years later, when Michaels was considering casting Ferrell at “SNL” in 1995, Ferrell came to their second meeting with a briefcase, which he rested on his lap and never opened during their conversation. As their meeting concluded, Ferrell picked up the case and began to walk away. Michaels had to ask: What’s in the briefcase? Ferrell popped the locks, revealing stacks of fake cash. He’d planned to mock-bribe Michaels with the money during the interview but aborted the idea when the conversation turned serious.

Ferrell knows people don’t get him. And he’s OK with that. “Adam and I have always been fascinated by that type of humor that hopefully most people think is funny, but if there’s 25 or 30 percent, even 40 percent, that don’t get it, that tickles us almost more than the 60 percent that are laughing really hard. I don’t know what that says about us or me.”

Well, he ventures, maybe it says that comedy isn’t universally understood or appreciated. And if it is, it’s probably not that funny to begin with.

Ferrell – his given name is John; William is his middle name – grew up in Irvine, the older of two boys (his brother Patrick is three years younger). Ferrell’s father, Lee, was a musician who played with the Righteous Brothers for years and was rarely home during his sons’ formative years. He divorced Ferrell’s mother, Kay, a schoolteacher, when Will was 8, but moved nearby.

Ferrell, his mother and brother lived in an apartment complex called Park West, a place that Ferrell describes as pleasant but one known among his more affluent peers as “Park Watts,” primarily, Ferrell suspects, because it was home to the few minority families in town. Ferrell describes his upbringing as “definitely lower middle class. It’s not that we ever went without, but it was definitely always tight.”

Despite his comedy stardom, Ferrell, like “SNL” alums Bill Murray, Adam Sandler and Ben Stiller, has branched out into drama, too. The public response has been mixed, though critics have generally liked Ferrell’s work. Ferrell starred as a down-on-his-luck salesman in “Everything Must Go,” which was released in May to favorable reviews but scant ticket sales (maybe, Ferrell says without bitterness, more people would have seen it if it had had “a 3-D element or possibly a precocious animal in sunglasses”).

“Stranger Than Fiction,” which Ferrell starred in with Emma Thompson and Dustin Hoffman in 2006, did better at the box office. But another Ferrell drama, “Winter Passing,” in which he played a struggling musician, came and went a few months earlier without much notice at all.

Ferrell shrugs. Whatever.

“The victory for me is getting to do something different,” he says. “The bonus is the nice reviews.”

For years, he says, he harbored enough doubts about his career that he maintained a running joke with his wife, Viveca (with whom he has three young sons): “I’d write down a list of alternative occupations I could do if the mayor of show business called and said, ‘We’re kicking you out of town.’ I’ve always felt like I’ve snuck into a black-tie party with a Sears Sans-a-Belt leisure suit on and no one’s noticed I’m holding a glass of champagne. I was always waiting for someone to notice and say, ‘You’re not supposed to be here.’ ”

Not very darn likely to happen now.

Besides, how much fun would the party be without him?