The dogs pile out when we reach his canyon trail off Mulholland Drive. Cooper is six feet three, 185 pounds, and none of that is fake-out movie-star muscle: He rowed heavyweight crew at Georgetown. He starts off at an easy, conversational jog on the gravel ridge road, but about a mile and a half later I've run out of conversation and he's just getting warm. "Want to try the mountain route?" he asks, pointing at a steep billy-goat path crisscrossing the peaks on either side of the road. Soon he's racing away, with his happy rescue dogs, each with 98 dog years of hard living, pacing him over the hills.

"It's an unusual situation," Ed Helms says of his Hangover costar. "Bradley is a highly intelligent being wrapped in a hot, studly body." Zach Galifianakis sees a different side. "He likes to nap," he says. "He'd come over to my trailer and ask if he could nap near me. It was weird. The first time he did it, I was in my trailer, running my mouth about how my sneakers looked like something Paula Poundstone would wear. After 12 minutes of monologue I look over and I'd bored Bradley into the cutest nap face the world has ever seen. Twenty minutes later he woke up and we chewed tobacco."

After the run, we drop by Cooper's house—an indoor-outdoor Craftsman-style one-story that he recently finished renovating. Now that he has a number of projects in the pipeline, he's finally splurged on some real estate. In addition to The Hangover, this year he's starring in New York, I Love You and All About Steve, opposite Natalie Portman and Sandra Bullock, respectively. The bathroom has those black meditation pebbles; the front and back yards are stocked with flowering vines and ficus trees, a koi pond (minus the koi, which raccoons got), a Japanese-style hot tub. Except for the two flat-screen TVs, above the fireplace and in the converted garage out back, it's the kind of L.A. bachelor pad a samurai might live in between shoots.

The walls are hung with art photographs, but half of what he's got up are old family black-and-whites—of his mom, Gloria, and dad, Charlie, a Villanova basketball star turned Merrill Lynch stockbroker (now retired), of his grandpa Angelo Campano retiring from the Philadelphia Police Department. "Beat cop the whole time," Cooper says. "Never shot his gun—he was always proud of that. I still have his billy club." He pulls a scuffed wooden nightstick out of the closet and hands it over. I ask whether his grandfather ever used it on him. "Never hit me," he says. "But there was a lot of belt threatening."

Even his appetite is old-school. Every Saturday his grandma Assunta used to make southern-Italian specialties for the following week—handmade pasta, ravioli, cavatelli—and Cooper cooked right along with her. According to his older sister, Holly, cooking was how Bradley spent vacations as a kid. "He'd get up in the morning and make himself a huge breakfast," she says. "Eat it, clean it up, start making something for lunch, pasta or stromboli, that he'd make himself. Then he'd clean that up and start working on a snack."