"Is death or mortality something you think about or you're fearful of?" Bradley Cooper, the star of The Hangover, asks as he crosses the parking lot of a Ralph's supermarket in Venice, California, in April. Cooper, best known for playing "Sack" Lodge, the summer-house bully who body-slammed Vince Vaughn in Wedding Crashers, likes mixing in conversational drop shots like this. Last night, for instance, between his first and second order of steamed clams, he asked, "Do you like people? Do you have an interest in people?"

It's easy to fall for his big servings of brotherly love, equal parts laid-back L.A. and Philly Italian. According to his mother, this amiability made his schoolteachers so suspicious they used to ask her, "Is your son trying to pull something?" But the thing you forget—at least I did—is that the 34-year-old Actors Studio grad has arrived at the brink of superstardom thanks primarily to his dead-on comic timing. As I launch into a story about a talk I had with my dad on his deathbed a few years ago, Cooper stands by the door of his Mercedes truck listening, unwrapping his recent Ralph's purchase, and flossing. Halfway through my story he starts moaning: "Oh . . . mmm . . . Wow, was that great!"

He gets into the truck and starts it. "You're talking about your father's death!" he laughs, then begins Take 2 of the flossing scene. "'Oh, man—that clam I just got out. Jesus Christ, Kevin. Oh, that's bliss!'"

Hollywood careers can start in unexpected places—John Wayne's first (uncredited) role was an Ivy Leaguer, George Clooney made his film debut opposite an animatronic bear—but Cooper is genuinely surprised that he's coming in via the comedy entrance. "I'm not even funny at all," he says. "That's what's so ironic." He leans over the console in his truck. "I'm kidding. I have my reel. I'll show you." Then, after a beat, "I'm kidding." He grew up idolizing Robert De Niro and Daniel Day-Lewis, not Bill Murray and Steve Martin. If anything, he says, he felt suited to "Harrison Fordish" real-guy action roles. But the instant he admits this, he sends himself up again. "Just because when I was a kid, I would fake-fight all the time. I was really good at the sound effects. That's the reason why I thought I could be effective in this business."

The Hangover, which opens right in time for wedding season, is a departure from the man-boy comedies of recent vintage: Three guys at a Vegas bachelor party wake up on the floor of their Caesars Palace fantasy suite to learn that they've lost the groom, along with any memory of the night before. The unlikely trio of leads—Ed Helms (Andy from The Office), Zach Galifianakis (a veteran of the stand-up circuit who has played a bunch of homeless guys), and Cooper—are perfectly mismatched: Helms plays the flustered romantic, Galifianakis the tagalong misfit, and Cooper the instigator with buckets of bad advice. Or as Helms puts it, "the uptight nerd, the weirdo, and the alpha-male cool guy." Warner Bros. feels so confident about the movie's box-office prospects that, even before the opening, it signed on for a sequel.