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 will hand the award to Ferrell tonight in one of those made-for-TV gala-specials (it will air on PBS stations Oct. 31), 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!”

No trace of cruelty

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.

As McKay points out, Ferrell has played the full range, from subtle to slapstick to utterly bombastic. He’s been the damaged man-child (“Elf,” “Step Brothers”), the aggressive dope (“Old School,” “Wedding Crashers”), the pompous and oblivious alpha male (“Anchorman,” Bush).

If that weren’t enough, Michaels, who’s been managing star egos like a lion tamer for decades, says Ferrell is that rare comedic commodity: a low-maintenance mensch. “People adored working with him” at “SNL,” says Michaels, himself a Twain recipient. “He was never funny at someone’s expense. There’s not a trace element of cruelty or meanness in Will.”

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. Ferrell built on his burgeoning interest in comedy by creating humorous skits for his fraternity brothers. He also found a bigger stage with the help of a humanities teacher, the late Ron Gottesman. Midway through one of Gottesman’s lectures, Ferrell would casually wander into class pretending to be a campus handyman.

“Excuse me, what are you doing?” Gottesman would ask, as Ferrell, smoking a cigarette, would start working away with a power drill or a bucket and mop.

“Don’t worry. I won’t be long,” Ferrell would reply breezily. He always made sure to bend over far enough so the class could take in his “plumber’s crack.”

Branching out

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 rarely lost his nerve after that.

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.”