Sean Parker was sitting in World Civilization class at his Virginia high school when someone brought him a note. His father, it read, was waiting to take him to an orthodontist appointment. A chill ran down Parker’s spine. He didn’t have an orthodontist. When he got outside, his father angrily whisked him into the family minivan. When they arrived at their modest suburban house, a team of F.B.I. agents was toting papers and a desktop computer out of Sean’s room.

Within a few short years, Parker went from apprehended 16-year-old hacker—he had managed to break into the computer networks of numerous multi-national corporations and even military databases—to world-class Internet entrepreneur. In 1999 he became rather notorious, at 19, for helping an even younger teenager named Shawn Fanning create Napster. That free song-sharing service upended the music industry. More recently, Parker played an indispensable role as the founding president of Facebook, the mammoth social-networking site where 500 million people now spend 700 billion minutes a month. Had he not joined founder Mark Zuckerberg in Palo Alto in the summer of 2004, when the fledgling Facebook was just five months old, the service almost certainly would not be the colossus it is today.

Parker is widely considered a Web oracle; more than a few acquaintances and colleagues use the word “genius” to describe him. He understands not only computers and Web networks but also how people want to incorporate them into their lives. As a result, he’s been stunningly successful. That said, he has a libertine side. Parker has a knack for missing deadlines and appointments, for disappearing for weeks on end, for avoiding the press. (His decision to cooperate with a Vanity Fair profile is unprecedented and rather out of character.) He was pushed out of Facebook after an arrest for cocaine possession in 2005. (No charges were filed.) Even among his many supporters, he has a reputation for being an erratic party animal.

Now he is about to achieve a new level of fame, as one of the main subjects of the highly anticipated film The Social Network. In theaters this month, the movie purports to tell the story of Facebook’s first year, partly by focusing on a darker side of Parker’s persona. Justin Timberlake plays a suave, conniving Parker, who both in the movie and in reality was Zuckerberg’s main mentor during Facebook’s crucial early days. But as crafted by screenwriter Aaron Sorkin, Parker comes across as a pushy, greedy—and, yes, visionary—schemer. “A million dollars isn’t cool,” Parker says at one point in the movie. “You know what’s cool? A billion dollars.” Zuckerberg, played by Jesse Eisenberg (see page 189), comes across as cocky, angry, and somewhat sex-obsessed.

The real Parker is both more complex and more interesting, despite the considerable skills of Sorkin and director David Fincher. In fact, Parker, a svelte, wavy-maned clotheshorse, is a uniquely quirky figure in the annals of 21st-century business. At age 30, he is already worth close to a billion dollars, thanks mostly to the cache of Facebook stock he still owns. An autodidact who barely finished high school, he is nonetheless almost painfully cerebral. A sickly child whose asthma sometimes landed him in the hospital, he devoured books from a very young age; his father, a U.S.-government oceanographer, began teaching him programming at age seven. There is hardly a topic—literary, political, medical, or technological—about which he cannot offer an informed and nuanced opinion in his rapid-fire patter. (Don’t get him started on Ben Franklin’s role as a media pioneer.)

Most of all, he turns his knowledge and instincts toward Internet business strategy as a way, he says, of “re-architecting society. It’s technology, not business or government, that’s the real driving force behind large-scale societal shifts.” Indeed, Parker has such a superb track record for predicting where technology is headed (and which type of product and service will appeal to consumers) that companies often invite him to invest simply to tap his brain. “Few people are as smart as he is,” says Facebook’s Zuckerberg, aged 26, who still consults quite frequently with his former partner.

But, for all his Web-world savvy, Parker at times seems just as drawn to recreational indulgence. His is the life of programmer-as-rock-star—often spent among real-life rock stars—with the lifestyle that that implies. He routinely stays up very, very late, talking intensely about subjects he cares about and/or partying—and sleeps in much of the following day. Says San Francisco tech investor Ron Conway, a longtime friend, “The fact that Sean is so scattered yet so brilliant is something you just don’t see often. He’ll probably start another five really significant life-changing companies before he’s through.”

Parker’s high-school hacking bust seems itself cinematic: a down-home version of a Matthew Broderick scene from WarGames. The teenager had been sitting in the family den, all night, drilling deeply into the bowels of a Fortune 500 company, which he refuses to name. Back then he had a hobby, he says, of hacking into different sorts of organizations, keeping a file of .com, .edu, .mil, and .gov Internet domains he had penetrated in various countries around the world. His goal was to break into one of each type in a laundry list of countries. He claims that once inside he usually alerted the system administrator—from his or her own e-mail—to vulnerabilities he had discovered.

Unfortunately, after this particular night, his father came downstairs at five A.M. Parker had been performing erratically in high school—sometimes pulling A’s but just as often simply refusing to work, and nearly failing. It was all deliberate, he claims. “I had a desire to prove to myself that I was actually in control—that I wasn’t a puppet,” he says. “I didn’t want to kowtow to the system.” Seeing his son hunched over his terminal, Parker’s father, outraged, apparently had a vision of yet another lost day at school. “So,” recalls Parker, “he grabbed the keyboard from my hands, ripped it out of the computer, and took it upstairs. I started crying and saying, ‘Dad! You don’t know what you’re doing! I have to log out!’ But he didn’t let me.” Unable to cover his tracks, Sean Parker’s dalliances were exposed, his location identified by tracking him through his Internet-service provider. In the end, as a minor, he was sentenced only to community service.

But one aspect of this story may help elucidate Parker’s subsequent attitudes toward rebellion. He performed his court-ordered duties at a library with other teenage offenders. There he met a girl whom he describes as a “punk-rock princess.” One day she wrote her phone number on Parker’s hand—in ballpoint pen, he remembers fondly—and a few months later, he says, “I lost my virginity to her.” He explains: “I thought it was an incredible cosmic irony. This was the most romantic experience of my life and I met her because I’d been raided by the F.B.I.”

Around the same time, Parker made the online acquaintance of 15-year-old Shawn Fanning, another talented hacker. Fanning recalls their first conversation. “Right away we were talking about things like theoretical physics. We realized we had a lot in common.” Along with a couple of buddies, the pair soon launched an Internet-security firm called Crosswalk, offering to advise companies that might otherwise have been their targets. It didn’t succeed. Parker, meanwhile, began working as a programmer at a major Internet company near his Virginia home, receiving academic credit during his senior year.

Against his parents’ wishes, Parker decided not to apply to college, and when Fanning told him about his plan to create Napster, he immediately asked to get involved, becoming a co-founder and contributing key ideas. He picked up and moved to San Francisco, having never before spent any time away from home, says his mother, Diane, a TV-advertising broker.

In its first year, the music file-sharing network gained tens of millions of enthusiasts. Parker soon became a habitué of nightclubs and raves. But in the process Napster drew the wrath of record companies, which launched an all-out legal assault. Within 14 months, a federal judge would order Napster to stop allowing users to download copyrighted material. E-mails that Parker had written, blithely discussing the likelihood that users were breaking the law, were enlarged and displayed in open court by industry attorneys. Though an appeals judge let the service keep operating, it was the beginning of Napster’s long, slow death. Parker himself was pushed out by Fanning’s more elderly partners. Thus began a cycle of vertiginous triumph followed by humiliating failure.

In early 2001 he tried to launch his own Internet company, and to redeem himself. “It had to have the potential to be as big as Napster,” he says. “Otherwise it wasn’t interesting to me.” He realized his electronic address book was getting out of date. Maybe everyone could use help keeping theirs current. Could that be a company? But the idea took a while to gestate, and even longer to finance. “I lived on couches for something like six months,” Parker says. “I had no home. I was totally broke. I would stay at a friend’s house for two weeks, then move because I didn’t want to become this permanent mooch.” His girlfriend at the time urged him to give up and get a job at Starbucks.

Eventually, Parker and some partners managed to land some seed money from Sequoia, the prestigious Silicon Valley venture-capital firm. The company, named Plaxo, opened its doors that November. In short order it became the most famously annoying service on the Internet, peppering innocent Web users with requests to correct their entry in their friends’ address books. For the irreverent Parker, this was a virtue—a triumph of viral marketing. But disgrace soon followed. Parker’s unreliability began to grate on his colleagues and the company’s investors. Sometimes he didn’t show up for work. By early 2004 he was fired. The company’s board later hired a private investigator in a retroactive attempt to look into various rumors, including whether Parker had been providing drugs to other employees. Parker—who calls the accusations “ludicrous, a smear campaign”—was again on the street, and broke.

He began to hang around with some of his newfound San Francisco friends, including night owl Jonathan Abrams, a programmer who had launched Friendster in 2002, in part to help people hook up. Parker was fascinated with Friendster, which that year became the world’s first online social network to grow its membership into the millions. But the service began sputtering when its systems could not handle the traffic. Parker, however, smelled an opportunity.

One day—in a scene fictionalized in The Social Network—Parker saw Thefacebook, as it was then known, on the computer of his roommate’s girlfriend, a student at Stanford. (In the movie, he gets his first peek after spending the night with a woman whose name he barely knows.) Parker had already concluded that the most promising way to launch a social network would be within a relatively closed community. College seemed perfect. He trawled the Web site and sent an e-mail to the kid who ran it—Mark Zuckerberg, then a sophomore at Harvard—suggesting that the two of them meet.

Matt Cohler, who joined Thefacebook shortly after Parker, is awed when he thinks about that pivotal e-mail. “Napster and Facebook are two of the most significant companies in the history of the Internet,” he says, “and in both cases Parker spotted them earlier than anyone—other than the people who invented them.”

Parker impulsively flew to New York, where he met Zuckerberg for dinner, and the two quickly bonded. A few months later, in June 2004, they ran into each other on the streets of Palo Alto, where Parker, unemployed (but still driving around in a BMW 5-series), was living with yet another girlfriend. Zuckerberg invited him to move into Facebook’s newly rented summer house. At first, Parker slept on a pad on the floor of co-founder Dustin Moskovitz’s room, until, as Moskovitz puts it, “things got more serious with my girlfriend, and I had to kick him out.” Perhaps more than at any other time in his life, Parker focused closely on one project.

Back then Parker apparently believed even more passionately in the company’s potential than did Zuckerberg himself. Peter Thiel—the billionaire hedge-fund manager and co-founder of PayPal, who became Thefacebook’s first investor—says that around that time “Sean consistently argued that Facebook was going to be really big. If Mark ever had any second thoughts, Sean was the one who cut that off.” In late August 2004, Zuckerberg and Parker went into a branch of Silicon Valley Bank to open a business account. With only two weeks before the fall semester, Zuckerberg was still talking about returning to Harvard, and the two argued over it right then and there, according to Ken Loveless, a senior vice president at the bank. Parker was adamant that Zuckerberg shouldn’t go back. (Zuckerberg dropped out.) Says Moskovitz, known for his dry humor, “Sean probably deserves less credit for turning Facebook into what it is than he thinks he does, but also more credit than anybody else thinks he does.”

Besides serving as Zuckerberg’s comrade-in-arms, Parker also worked to bolster his partner’s position, so what happened to Parker at Plaxo could never be repeated at Thefacebook. In the financing that Parker negotiated with Thiel, as well as a much larger deal signed seven months later with the Accel Partners venture-capital firm, Parker was able to negotiate for Zuckerberg something almost unheard of in a venture-funded start-up: absolute control for the entrepreneur. Because of that, Zuckerberg, to this day, allocates three of Facebook’s five board seats (including his own). Without that control, Facebook would almost certainly have been sold to either Yahoo or Microsoft, whose C.E.O., Steve Ballmer, offered $15 billion for it in the fall of 2007—only to be met with a blank stare from the then 23-year-old Zuckerberg.

Yet again, Parker’s undisciplined ways would prove his undoing. On a kiteboarding trip to North Carolina in 2005 he was arrested during a party at his rental house on suspicion of cocaine possession. Though he was never formally charged, some of Facebook’s investors and employees felt Parker could no longer effectively serve as company president. With much anguish, he agreed to depart.

But while his exit may have been ignominious, Parker, by this time, was getting better at rolling with the punches. This was due, in part, to the fact that Zuckerberg himself never forsook him. “I don’t think Sean ever really left Facebook,” says board member Thiel. “He’s continued to be involved in many ways.”

Working with Parker, according to several colleagues, remains gratifying but frustrating. Joe Green, a Harvard classmate of Zuckerberg’s, who is now Parker’s partner in a Facebook application called Causes—which helps people donate money to nonprofits—first met Parker six years ago at Facebook’s Palo Alto crash pad. “I was sleeping on the couch,” Green recalls. “Sean came in and needed to borrow money for a haircut.” Once, Green says, when the two of them were late for a flight, Parker simply refused to stop doing his e-mail. “He said, ‘I’m getting a lot done. It’s worth it to me.’ ” At times, Green insists, the only way to reach Parker is via “war dial”—calling his cell phone 10 to 20 times until Parker, who seldom listens to voice mail, finally realizes somebody must really want to talk to him.

Reid Hoffman, a longtime friend and the founder of LinkedIn, who sits with Parker on the board of Gowalla—a location-based social-media service—remembers Parker suggesting an intriguing new concept for the company while the two of them were chatting in Davos, Switzerland. “I said, ‘Dude! You gotta start coming to board meetings again!’ This is Parker’s pattern—great idea, work like the devil, then disappear for a while.”

“Why do we all put up with it?” asks Green rhetorically. “For two reasons. He adds a lot of value in the time he’s there. And he’s very loyal. When you really need him, he will be there. That builds up a reservoir of goodwill.”

Reggae plays in the background at Shawn Fanning’s huge 40th-floor apartment, directly over San Francisco’s Bay Bridge. It is late at night. Parker stretches back on an easy chair and bemoans what he sees as the scarcity, in contemporary culture, of revolutionary thinkers on the level of, say, Jim Morrison and Jack Kerouac. “They were capable of folly,” he says, “and willing to take risks in terms of their message. We live in an extremely repressive era, and we fail to realize how repressive it is, because we’re told that all these outlets for rebellion, like listening to rock music, are no longer satanic. Smoking weed—that’s sort of O.K. and acceptable in some circles.” To Parker, the implication is that people in his position have almost an obligation to do what they can with the tools at their disposal—software and the Internet—to free up society through disruptive technology. As he muses, it is clear that he sees entrepreneurship and invention as handmaidens of social transformation.

Parker had been trying to explain himself while he wandered the streets on that hazy night, attempting at length to find Fanning’s apartment (even though the building is the tallest in the neighborhood). “I think the best way to describe me is as an archetypal Loki character,” Parker begins, “like Joseph Campbell’s Hero with a Thousand Faces. I’m like the prankster or Puck in mythology. He’s not trying to cause harm, but rather to pull back the veil that masks your conventional, collectively reinforced understanding of society. This renegade thing was very clear at Napster. The point was that the emperor—the content industry—had no clothes.” He hesitates. “This all probably sounds incredibly pretentious and narcissistic.”

It does. But even as Parker alternates between putting himself down and pumping himself up, he can rely on most of his friends to speak glowingly. Says Peter Thiel, “I’ve told Sean he may be the long-lost grandson of Howard Hughes—a brilliant entrepreneur who is somehow transforming the United States and yet is not understood by society. Sean is one of the great serial entrepreneurs of his generation, someone who is really changing the world and turning the wheel of history.”

It’s easy for Parker to make new friends, and he does quite often. People of all sorts are captivated by his ideas and his enthusiasm. “Sean is a genius, no question,” says Ashton Kutcher, whom Parker advised while the actor was developing his own Net-oriented production company. Wikipedia founder Jimmy Wales met Parker in 2008 and the two started hanging out. “He gets things very quickly,” says Wales. “He’s incredibly intense and engaged about ideas.” One of Parker’s closest friends, musician Sean Lennon, offers, “His brain is like the technological equivalent of the Library of Alexandria. He’s really one of the smartest people I’ve ever met—and that’s an understatement. He’s always talking about the potential of computers to generate algorithms for likable melodies, and we have this ongoing argument: he believes it’s only a matter of time before computers will be able to create listenable tunes. Sean is an artist—a business artist.”

Actress and activist Trudie Styler, who is married to Sting, invited Parker and his then girlfriend to a retreat for philanthropists and activists that the couple hosted at their Tuscany estate last year. There, Parker met Laura Ziskin, who produced the Spider-Man movies and co-founded a charity called Stand Up to Cancer. “It turned out Sean has an interest in immunology and a belief that it is the next frontier in cancer research,” says Ziskin. “He had talked to as many people about it as I had!” They’re now friends. Styler found herself impressed: “He was just so lovely with everyone, and kind. A higher being. I’m very fond of him.” (Parker also fraternizes in the most elite precincts of global governance and policy—but in his own way. At the World Economic Forum in January, he was disappointed in the quality of the nightlife in Davos and speculated with relish that he could throw the all-time-best forum party if he took over a big local venue and brought in some of his rock-star friends.)

A lover of the good life, Parker maintains a collection of elegant white shoes, a closetful of Tom Ford suits, and a $100,000 Tesla electric sports car he never quite seems to have time to drive. He divides his nights between a San Francisco apartment and a palatial (rented) New York town house. Among its many amenities: a full, mowed lawn on a patio on the third of its five floors.

And although he thinks little of hiring a private jet for a late-night trip from New York to Washington, he is also almost compulsively benevolent. When his friends fund-raise for charity, several told me, Parker is often the one who contributes the most. A connoisseur of tea (he has a collection of about 100 varieties), he makes gifts of his favorite blends, which he personally labels and presents in special mulberry-bark canisters ordered from Japan. He has financed the businesses of numerous cohorts, merely out of affection. “He’s one of the most generous people I know,” says another associate. “Also one of the flakiest.”

Today, Parker spends most of his time finding and managing investments for Founders Fund, Thiel’s venture-capital shop. His current passion: a London-based music company called Spotify, which he thinks can finish the job that he and Fanning started with Napster—this time, legally. (Spotify lets you listen to music from almost any artist on any label, gratis, through ad-supported streaming.) Not everything Parker touches, however, necessarily turns to gold. A little while back, he was shelling out money in an unsuccessful bid to expand a hand-painted-clothing company. He was also briefly brainstorming with a group that included his old crony Shawn Fanning and the 18-year-old founder of Chatroulette, Andrey Ternovskiy, about how to turn that voyeuristic live-video networking site into a full-fledged service. Oh, and when he’s home in New York he takes piano lessons from Sean Lennon.

While Parker has few generational equals in terms of raw achievement, that doesn’t mean he isn’t still surprisingly insecure. As several bemused friends and associates recounted, he devoted considerable effort—knowing a reporter would be interviewing them for this piece—to attempting to script their comments. (Mostly, they say, he appears to have wanted them to characterize his wilder behavior as youthful indiscretions.)

“If there’s some triumphant end of the story, I guess in a roundabout way I’ve gotten what I wanted,” Parker posits late one night, “which is the ability to do interesting things and the wealth to be free.... I can sort of do what I want. Maybe I have to work harder to prove myself in some new relationship because they’ve heard some wacky stories about me. But at least I can get the meeting.”

The road, he points out, has been rocky. “It hasn’t been some kind of fairy tale for me. All of my success has been born of failure. Your childhood dreams are always tales of glory; reality is a lot messier and more dramatic.”

Parker met his on-screen alter ego, Justin Timberlake, just once—at a club, after the actor had read Aaron Sorkin’s script. “He said he wanted to get to know me,” recalls Parker, “but I said, ‘That isn’t going to help you play the part Sorkin has written. That character really isn’t me.’ ”

True. Sorkin’s Parker is vindictive, calculating, and mean, unlike the real one. The Parker of the script is also greedy, which is not Sean Parker’s big issue. More than money, he wants credit and recognition. “I’ve helped change the world, at least three times,” says Parker at one point, by way of self-assessment. But he also says, wistfully, “I’m a perennial outsider.” With the movie likely to be a hit, one thing is certainly going to change. He’s about to get the kind of recognition that the superficial society which he scorns seems to value the most: the stamp of real celebrity. How he handles it is another question.