Geico is known as much for its offbeat ads as it is for its discount auto insurance. It targets older customers with campy spots featuring aging stars—Little Richard, Charo—who knowingly play off their washed-up status. Geico’s other mascot, that maddeningly chatty gecko, is seemingly everywhere you look. (The gecko is supposed to help people remember the company’s unusual name.) But the caveman spots—which feature urbane, effortlessly cool proto-humans who are deeply offended by Geico’s “So easy a caveman can do it” slogan—have gotten most of the attention, especially among young people. The ads achieved cult status, partly thanks to YouTube, and partly because of Geico’s saturation of the airwaves. Between its various campaigns, the company spent $499 million on advertising last year, according to TNS Media Intelligence, a market-research firm.

The ads have been so successful that the cavemen now have to fend off groupies. After filming a spot in Los Angeles last year, Lehr and his two caveman colleagues (actors Ben Weber and Jeff Daniel Phillips) were mobbed by fans as they ambled down Sunset Boulevard in their costumes. “It was like the Beatles had walked out,” says one of the commercials’ directors, Josh Gordon. This year, Lehr attended an Oscars after-party as the caveman and was swarmed by more admirers. “There was an incredibly gorgeous woman who came up to me and gave me her phone number,” says Lehr. “The paparazzi wanted to take pictures with me.” A Web site, cavemancrib.com, even lets fans “tour” one of the characters’ apartments and scroll through the songs on his iPod.

As if the poor guys weren’t already in danger of overexposure, along comes ABC, which has ordered up, cringe, a sitcom pilot centering on the awkward lives of the out-of-time characters, who will live in Atlanta and date beautiful women. “It’s every advertiser’s dream, a walking, talking commercial that’s a 30-minute program,” says AdWeek critic Barbara Lippert.

If it works. The cavemen—like Geico’s other mascots—were the inspiration of the Martin Agency, an ad firm in Richmond, Va., that counts Wal-Mart, Hanes and UPS among its clients. Geico sells insurance directly to customers, so it wanted ads that promoted its toll-free number. But there was a problem: insurance is boring. “We know that interest in our category is extremely low,” says Ted Ward, Geico’s vice president of marketing. “Our competitors start by talking about car insurance, and that’s when people tune out.”

So Martin developed ads that aimed to entertain. The caveman spots are scripted, but the actors are encouraged to improvise. In one ad, a Geico spokesman tries to appease the insulted cavemen at a trendy restaurant. Hirsute and surly, the cavemen are also comically refined. One sports a soft pink linen jacket and shades perched atop his oversize head. “I’ll have the roast duck with the mango salsa,” he tells the waiter with studied nonchalance. The actors did take after take of that scene, trying different foods until they found just the right one (the runner-up line: “Do you guys still have those little pizzas?”).

But a gag that works so brilliantly in 30-second snatches could grow tiresome when stretched to half an hour. This isn’t the first time the entertainment industry has tried to make something more of a popular ad. In 1989, CBS aired a Saturday-morning cartoon based on the dancing California Raisins. Domino’s Pizza released a Nintendo videogame based on Noid—its now defunct Claymation pizza pitchman. Remember those? Didn’t think so.

Flop or not, Geico’s admen are already preparing for a post-caveman era. As the fourth largest car-insurance company in the nation, its share of the market is only 6.3 percent (industry leader State Farm is at 17.7 percent). The next shtik features a preteen boy named Lauren Wallace, who yearns to make it as a NASCAR driver. The fictional “third cousin, once removed” of real NASCAR driver Mike Wallace, who races Geico’s sponsored car, he careens through the grocery store with a shopping cart. It’s cute, kind of. But coming on the heels of a terminally hip Neanderthal, pretty much anything is going to seem like a letdown.