With the exception of Michael Jackson, celebrities always seem more normal in real life than you'd expect, just as they almost always seem shorter. It's a surprise when someone you've seen on a big screen and on posters appears in a hotel room, pacing and holding a cordless phone.

You don't imagine someone like Matt Damon eating his breakfast (or, more precisely, smoking his breakfast) inside a suite at the Ritz-Carlton that's starting to smell like a sports bar. You imagine him standing dramatically at cliff's edge, staring into the distance with troubled eyes, but you do not imagine him clicking off the phone and asking why radio personalities have to be so loud in the morning, or looking weary -- why are movie stars on press junkets always so weary? -- or sitting in the suite's dark office and flicking the ash of his Natural American Spirit into a saucer.

He starts telling you about how he spent the night before in Boston, where his new movie "The Bourne Supremacy" was being screened, and how his whole family was there and he'd missed them so much he didn't want to leave, and he pushed back his flight and got in at 2 a.m.

Damon's hair these days is short and jagged, not at all like the floppy blond cut he sported in the late '90s, when he became popular with "Good Will Hunting" and "The Talented Mr. Ripley." Back then, he looked like a rough-hewn, more masculine version of Leonardo DiCaprio, with the same squinty blue eyes and boyish quality. With his jaunty nose and jutting ears, he looked clean-cut and all-American and a little like Dennis the Menace all grown up, and hot. Now, at 33, Damon's face is more angular. There is a little gray at his temples and grooves around the mouth when he smiles. A light stubble traces the sharp lines of the jaw and dusts his upper lip.

Damon has variously been described as the nice guy, the boy next door, apple-pie. And while clearly this has to do with the ears and the eyes and the big white teeth, Damon says he thinks it's also connected to the way he behaves during interviews. There are few professional duties he hates more than conducting the shallow, five-minute Q&A's required for movie promotions. Some time ago, he says, a friend advised him to come up with an "alter ego" for these interviews, "so your soul doesn't get, y'know, robbed by doing these things." He calls this personality Mike Smiley, and says that when he watches footage of these interviews he sees Mike Smiley instead of himself.

"I can't stand to look at it; it doesn't feel like it's who I am," Damon says. "But it feels like the person who's being as polite as possible and just trying to get the thing over with."

Then, Damon seems to catch himself. He does not mean to suggest he's not enjoying this interview. "These are a little different because they're a little more substantive," he says. "There's a big difference between an hour interview and five minutes."

Damon's publicist has brought in oatmeal but he doesn't eat it, saying that his stomach is just waking up. You figure he's being polite. He offers his guest a cigarette, then he corrects himself for offering, then gets up to grab another and offers to stand in the doorway so as not to offend his guest with smoke.

You wonder whom you're getting. Is this Matt Damon or Mike Smiley? If this were not an interview, would Damon be ripping the filters off his American Spirits and eating oatmeal with his fingers? Or is Mike Smiley the condensed-milk version of Matt Damon -- sweeter, thicker, but the same basic substance? Just as careful, just as solicitous? At last, you bum a cigarette and he leans over to light it.

"I smoked Camels for years," he says, before switching to a brand known as the "natural cigarette."

"It's amazing. I mean y'know, it's about 350 additives your average cigarette has, I mean from arsenic, from cyanide to ammonia."

It's as if you and Matt have a special connection, ashing into the same saucer, talking about your lefty moms, sharing anecdotes of India, laughing at Matt's foibles together. Ahahahaha! What a normal guy!

Poor Mike Smiley, with his sucked-out soul.

Family Ties

Matt was 2 when his parents divorced, though they remain on friendly terms. On Christmas Eve, when he and his older brother, Kyle, were growing up in Cambridge, Mass., their father used to sleep over on the living room couch on Christmas Eve, so he'd be there when they woke up.

Dad is now retired, having worked as a stockbroker, schoolteacher, then in the business of helping corporations invest in low-income housing. Their mother is a professor of early childhood education at Lesley University who tried to talk her kids out of watching TV. She often took notes on the boys, using them in her studies. For several years she and her sons lived in a communal home with five other families in Cambridge.

In his adulthood, Damon's mom has been a careful, sobering influence, viewing his celebrity with a wary eye, worrying that it might make him into a "commodity," as she once put it, a "cog in the capitalist system." She once said that before her son appeared on the cover of Vanity Fair in the late '90s, she'd never seen the magazine.

Damon has inherited his mother's progressivism, which in Hollywood makes him utterly unremarkable. He stumped for Al Gore's campaign. He's read Michael Moore's "Stupid White Men" and a polemic called "The Best Democracy Money Can Buy," and says he'd happily return the "millions and millions of dollars" that Bush's 5 percent tax break gave him to "get some of the social programs back." He recently did some voice-overs for Fleet Bank and -- after consulting his family on how best to give the money away -- donated it all to organizations working for peace and conflict resolution.

Damon has credited his mom's focus on "open-ended play" with helping him discover his love of acting as a kid, and helping his brother, now a sculptor, develop his own creative spirit. Kyle would make his brother costumes -- a bionic arm out of construction paper, for example -- and Matt would wear them. Kyle created; Matt became.

This is the story of how Matt broke his leg:

"Do you remember Shazam?" he asks. He talks about a childhood superhero who, "whenever he needed his superpowers, he'd call 'Shazam' and suddenly he'd be transformed and he could fly and stuff like that. And so, I was on top of a jungle gym with my towel around my neck and I screamed 'Shazam!' and jumped. I think I was 3 years old."

Perhaps it's silly to read into this incident. People are always trying to psychoanalyze celebrities, and how much can you interpret from a 3-year-old's behavior, anyway? Still, you find yourself considering the stories you've heard about Damon's intensity as an actor, and wondering if his ability to believe in his own transformations is what makes him good. Because he is good.

Remember him in "Ripley"? (Please don't remember him in "Stuck on You," wearing those awful bangs, playing a conjoined twin for comic effect.) As Tom Ripley, Damon was so pasty, so selfish, so needy, so creepy, that he actually became ugly. Remember that awkward stance, those too-big glasses atop a nose that -- next to Jude Law's delicate features -- looked crudely fashioned? Remember him on the beach, wearing a pair of lime-green bathing trunks, pale amid golden bodies? Remember his blank stares and his rows of gleaming, barbaric teeth?

Ripley kills several people in that film. Damon says he came to believe fully in his character's rationale for these murders. He says that when he watched a completed version of the scene where Ripley walks toward Gwyneth Paltrow's character with a razor blade, he was angry when he heard the scary music that director Anthony Minghella had layered over it.

"Anthony was so deeply involved in Ripley's point of view also, and he and I were connecting in that way," Damon says. "So to see Ripley doing something and to know that Anthony had put this music on it was almost like editorializing negatively something that Tom was doing that made total sense to me and I know made sense to him. . . . It was alarming to me how deeply I felt that sense of betrayal."

Damon talks about himself as compulsive, with a mind-set that's "all or nothing." For "The Rainmaker" (1997), Damon tended bar in Knoxville for about a month to acquire the right accent. For "Courage Under Fire," which came out the year before, he lost 40 pounds by running 13 miles a day and eating a diet of chicken, egg whites, potatoes and other vegetables. He did it without the supervision of a doctor and inadvertently induced what he has described as an adrenaline disorder, for which he had to take medication.

For "The Bourne Identity" (2002), based on the Robert Ludlum books, Damon took up boxing and martial arts training, and for "Supremacy," the sequel, due out on Friday, he kept up the boxing. In both movies Damon does most of the fight scenes himself, to make them more believable -- this time, he threw out his back. He was lifting an opponent "and slamming him back and spinning around with him and, y'know, I just should've maybe reached down and touched my toes once or twice before I did that," he says. "It was pretty much my own fault."

Damon has said he likes the Bourne series because it is character-driven, setting it apart from more vapid action movies. In both of the Bourne movies, you observe some of Jason Bourne's thought processes. He is clever but not indomitable. Instead of magically knowing where to go when he's speeding along in his car, he studies a map. In "Supremacy," Bourne's personality begins to take shape despite the amnesia that has plagued him since "Identity."

Still, an action movie is an action movie, the way Damon's mom sees it.

"I asked her if she liked it and she said, 'I did like it.' And she was trying really hard," Damon says. "The first movie she -- I don't think she'd ever seen an action movie and so she really didn't like it. . . . Last night, I think she was set up a lot better to accept it, but still she said, 'I got a little bit of a headache.' "

'Mattfleck'

It's hard not to compare Damon with Ben Affleck, with whom he entered mainstream consciousness in the late '90s with the success of "Good Will Hunting." They received an Oscar for the screenplay, and Damon was nominated for an Oscar for the title role as Will, the genius janitor of MIT.

Affleck and Damon grew up a few blocks from each other in Cambridge and shared a love of acting as kids. They are still best friends, and have collaborated on a number of projects, but their public images have diverged.

There was a moment last year when Affleck was asked if he was going to marry Jennifer Lopez, and he joked that he would marry Damon instead. The papers dubbed this Mattfleck. But Mattfleck -- the perception of Matt and Ben as peas in a pod, as conjoined twins, if you will -- had long since been killed off, in part by Bennifer.

While Damon was lying low, trying to stay normal, Affleck was showing up in Ms. Lo's music video and on celebrity magazine covers and in rehab -- embracing, it seemed, all the trappings of modern Hollywood stardom. While Affleck took on mainstream movies like "Bounce" and "Changing Lanes," Damon seemed to be more discriminating. There is real acting muscle behind Damon's face, while Affleck's charm is his face. Damon's "All the Pretty Horses," a disappointment at the box office, did not become a punch line like Affleck's "Gigli."

In short, you take Damon seriously. He went to Harvard before dropping out to pursue his dream. He does not come off as needy or too charming. He does not require you to love him and damn, that's appealing.

He talks about missing the ordinariness of his former life, and the way anonymity allowed him to be a fly on the wall when he was developing characters, and the way it allowed him to simply live.

"You have to preface everything by saying, 'Look, I'm not complaining, I'm incredibly blessed,' " he says. "But anonymity is something that is an incredibly valuable commodity and you're not aware that it's gone until it's gone. And the experience of it going, it's insidious. You meet people who've been famous for a long time and as much as they try and safeguard against it and as vigilant as they are about trying to protect their humanity, it has an effect."

For years he has been close-lipped about his love life. Privacy is next to normalcy, perhaps. After dating Minnie Driver and Winona Ryder, he has vowed not to date any more celebrities, or come as close as a cautious guy can get to vowing.

"It's always silly to say 'never' in these interviews -- then people come back and throw it in your face," he says. "But no, I can't imagine being in a position where I would -- I mean, my present situation notwithstanding, even if I wasn't in my present situation, even if I was single -- I can't imagine being with a celebrity. . . . It kind of magnifies exponentially the whole part of this thing that I don't like, and that really gets in the way of doing my job and interferes with the life part of life. I mean, just look at what happened to Ben."

Damon's "present situation" is with a single mom he met while she was bartending. They've been dating for about eight months. When asked about it, his face softens and he looks down into his lap. You can hear the smile in his voice.

"I mean, she's great. Without getting into it too much, she's, uh, she's yeah, she's great. She's a mom, and yeah, she's fantastic."

He looks like he'd like to say more, the way people in love do. "It's going well," he says. But he stops himself.

Matt Damon, star of "The Bourne Supremacy," clings to a remnant of privacy.Robin Williams and Damon, above, in 1997's "Good Will Hunting," in which Damon's friend Ben Affleck also appeared. At left, Damon and Affleck celebrate winning an Oscar for Best Original Screenplay for the film. In recent years, Damon and Affleck have taken different paths professionally. Damon in front of the Egyptian Theatre in Boise, Idaho, where he and producer Frank Marshall screened his new movie, "The Bourne Supremacy," to raise money for the Boise Contemporary Theater. Below, Damon and Julia Stiles in a scene from the film, a spy thriller.