It's the middle of the day in the middle of the week in Brentwood, the neighborhood O.J. put on the map. Judging from the bronzed beauties jogging the streets and the buff boys flitting about on $2,000 bikes, it seems like no one here actually has to work for a living.

Scattered about are those who do have to earn their keep. Like the young and not-so-beautiful ones serving caffeinated concoctions at the local tea joint. And then there's the youngish actor who's sitting there, anonymously sucking down a grande mate with soy. Lunch. His face is pancaked, his hair shellacked. One hand pats the shellac. Another clutches a cell phone, at the ready for the call that will summon him back to the set of his new movie, "Lucky 13."

You probably know his face, because Jeremy Piven is a journeyman actor who works all the time: "Black Hawk Down," "Old School," "Runaway Jury," "Scary Movie 3." Like today, for example. He's been at work since 6 a.m. He'll probably work until 7 or so, maybe even later. Not much glamour here. His trailer is the size of a closet. He tools around town in a battered Bronco, Coldplay CDs littered about the floor. In a town where even publicists have publicists, he travels sans entourage, an interesting dichotomy for a Hollywood actor who plays the agent from Hades in a new HBO series dubbed, appropriately enough, "Entourage."

Piven, 38, knows from entourages, having witnessed a few over the course of his nearly 20-year career. He's checked out the crew following Mark Wahlberg, ne Marky Mark, the actor/rapper/Calvin Klein undies model whose life serves as the inspiration for "Entourage." (Wahlberg is also the executive producer on the half-hour show, which debuts Sunday.) The two know each other from "around the way," a vantage point that has provided Piven a rich reference from which to mine his craft. There is, he says, a certain sweetness in the connection between Wahlberg and his buddies from Beantown.

"It's a group of guys he's known since childhood in Boston," says the Evanston, Ill., native who in person is both smaller and more handsome than he appears on-screen. (Last month, People named him one of Hollywood's hottest bachelors.)

"He's retained his loyalty [to them]. There's some nobility about that to me, within whatever your perception about an entourage is -- to make someone look more important, flashy, make an entrance, whatever. These are his friends that he's brought along for the ride. And I respect that."

He was intrigued enough to play Ari, a high-powered agent with an attitude problem. He's got a new client in Vince Chase (Adrian Grenier), a somewhat vacuous pretty boy who just happens to be the next Colin Farrell. Chase can't make a move, let alone read a script, without the input from his boys from back home in Queens: Turtle (Jerry Ferrara), a Hummer-driving numskull; Drama, his half brother (Kevin Dillon); and Eric (Kevin Connolly), a former pizza parlor manager who now works as Chase's manager.

Short-tempered and foul-mouthed, Ari is a man used to dealing with the upper echelons of the Hollywood pecking order, and he's none too happy about taking meetings with "Pizza Boy."

Says Piven of his character: "He'll snap your head off, reach into you, pull out your integrity, cackle and then . . . tell you how much he loves you in the next sentence."

The character was conceived specifically with Piven in mind, according to Doug Ellin, the show's creator, who'd been following Piven's career since his early days on "The Larry Sanders Show."

"We were lucky enough to get him," Ellin says. "He's got incredible timing and the ability to be likable and mean at the same time."

The personality dramas play out in comedic snapshots, with celebrity cameos and zingy one-liners that were frequently improvised, such as the scene where after a particularly contentious meeting between Ari and Eric, Ari decides it's time to kiss and make up. Or else.

"Do you want to hug it out?" Ari barks at Eric.

Eric declines. After all, who wants to hug a barracuda?

"Hug it out, bitch," Ari snaps, clamping his arms around Eric in a bear hug.

It's the sort of deliciously over-the-top obnoxiousness -- chock-full with hip-hop references and alpha male braggadocio -- that will keep insiders entertained trying to guess who is the real-life prototype for Ari. (Wahlberg has said the character is loosely based on his own agent.)

Over the years, Piven, of course, has encountered plenty of, um, inspiration for Ari. And how about his own agent? No luck getting Piven to dish. But he will grant you this: "There are so many agents that can be extracted from this guy. We could walk around this block," he says, gesturing around, "and gather up eight or nine agents and write four more seasons.

"If I can't find inspiration for this guy, I need to go back to Chicago and start cleaning tanning beds."

Nice dodge.

Indeed, he's cautious and guarded, a Shakespeare-trained actor who makes a living on camera but much prefers the relative anonymity of the stage. He's carved out a career for himself playing nasty and nice, of taking a shadow of a character and infusing it with enough vim and vigor to make the viewer sit up and take note: Who was that guy?

"It's your job as an actor to fill out the blanks," Piven says. "I love doing that. To fill in the bones."

He learned to act from his parents, Joyce and the late Byrne Piven, classically trained actors who ran the famed Piven Theatre Workshop in Chicago, which trained the likes of Jeremy and his sister and the Cusack clan. (Piven and John Cusack, best friends since childhood, have acted in a number of films together, including "Grosse Pointe Blank" and "Say Anything.") Theater infused every aspect of their lives. Sometimes this meant the edges between real life and the stage were blurred, such as the time Piven came home and found that his family's living room furniture was missing. He thought they'd been robbed, but his mother reassured him that they'd just needed the furniture for a staging of Chekhov short stories.

"I was so lucky to grow up in that household," Piven says. From his parents, he says, he learned the value of dedicating one's life to the perfection of craft.

Still, it wasn't a lesson that took immediately. Growing up, it was football, rather than theater, that held his fascination, recalls his mother.

The sport proved to be a formidable bargaining tool: Joyce let Jeremy play football, as long as he showed up for performances in their children's theater workshops. So it came as a bit of a surprise when Jeremy, by then a student at Drake University in Des Moines, called his parents to say he'd been cast as Mark Antony in "Julius Caesar." His parents were worried: Their son, the cutup, doing Shakespeare? How would he learn all those lines? What if he wasn't any good?

"He had his entrance. Banged open the door, ran up on the stage, just the way he would arrive for a football game," Joyce Piven says. "And he was wonderful. . . . We looked at each other and said, 'Oh, my God. We have an actor in our family. We were just floored."

From Drake, Piven moved on to polish his skills at New York University's Tisch School of the Arts (he dropped out his senior year to work as an actor), the National Theatre of Great Britain, the Eugene O'Neill Theater Center and Chicago's fabled Second City troupe, which nurtured such comic talents as Bill Murray, Dan Aykroyd, Harold Ramis and John Belushi.

"I'm a stage actor," Piven says. "That is what I do." A few months back, he starred in a production of the Sept. 11 drama "The Guys" in a fundraiser for his parents' theater group. Film affords him a comfortable lifestyle, but he says he'd love to find a home on Broadway. New York has its favorites, however, and he says he is not on the radar. Yet. As he sees it, for an actor, the comic and the tragic are linked. He's done Shakespeare and he's done "Old School." You've got to be a pretty competent dramatic actor to pull off comedy.

"Jackie Gleason was basically doing Greek tragedy in 'The Honeymooners,' " Piven says. "He was stalking the stage, fully invested, completely tragic, at times, an immensely angry, alienated rhinoceros being caged on that small stage. And it was hysterical."

Which is to say that Piven, though known for his comedy, seems to chafe at such pigeonholing:

"There are times in this town that you don't get a shot at something because they may have a reference for you which is one or the other."

For example?

"I can't go there, I can't do it," Piven sputters, shaking his head. "There's no way." Ever cautious, ever measuring his words. But he will say this: "All it does for me is make me work harder. That's all it does."

His cell phone rings, playing a riff from an old Biggie Smalls song. (Piven is a hip-hop head.) It's time to head back to the set, a sprawling Brentwood mansion. The film is a comedy about the competitive wars of bar mitzvahs. He shot eight episodes of "Entourage" in eight weeks, wrapped for the season one day and began filming "Lucky 13" the very next day.

That kind of pace doesn't leave much time for socializing, though he does try. Today he's dragging a bit because he couldn't pass up the chance to hang out at a John Kerry fundraiser. Because, well, he is a single guy and what better chance to meet and greet? But also because he' s into Kerry's politics, and he's signed up for the cause.

But for now, at least, politics will have to wait. There's a scant few minutes to park the Bronco and head back to that congested trailer. He pops back out, in costume, a blue shirt and tie. Just enough time to hop onto the van that will shuttle him and the crew to the set. Just enough time to grab a sandwich, get miked up and go.

To hear, "Rolling!" and start all over again, chasing the perfect take, the perfect line, the perfect moment of being perfectly in the moment. You know, working.

Jeremy Piven during a rare break from acting -- for lunch -- on the set of HBO's new series "Entourage."Jeremy Piven in his trailer on the set of "Entourage," a new HBO series in which he plays a high-powered Hollywood agent.Piven, as Ari Jacobs, has harsh words for Kevin Connolly's character in "Entourage." Although stage acting is his first love, Piven has had considerable success in movies including "Black Hawk Down," below.