Mark Zuckerberg founded Facebook in his college dorm room six years ago. Five hundred million people have joined since, and eight hundred and seventy-nine of them are his friends. The site is a directory of the world’s people, and a place for private citizens to create public identities. You sign up and start posting information about yourself: photographs, employment history, why you are peeved right now with the gummy-bear selection at Rite Aid or bullish about prospects for peace in the Middle East. Some of the information can be seen only by your friends; some is available to friends of friends; some is available to anyone. Facebook’s privacy policies are confusing to many people, and the company has changed them frequently, almost always allowing more information to be exposed in more ways.

According to his Facebook profile, Zuckerberg has three sisters (Randi, Donna, and Arielle), all of whom he’s friends with. He’s friends with his parents, Karen and Edward Zuckerberg. He graduated from Phillips Exeter Academy and attended Harvard University. He’s a fan of the comedian Andy Samberg and counts among his favorite musicians Green Day, Jay-Z, Taylor Swift, and Shakira. He is twenty-six years old.

Zuckerberg cites “Minimalism,” “Revolutions,” and “Eliminating Desire” as interests. He likes “Ender’s Game,” a coming-of-age science-fiction saga by Orson Scott Card, which tells the story of Andrew (Ender) Wiggin, a gifted child who masters computer war games and later realizes that he’s involved in a real war. He lists no other books on his profile.

Zuckerberg’s Facebook friends have access to his e-mail address and his cell-phone number. They can browse his photograph albums, like one titled “The Great Goat Roast of 2009,” a record of an event held in his back yard. They know that, in early July, upon returning from the annual Allen & Company retreat for Hollywood moguls, Wall Street tycoons, and tech titans, he became Facebook friends with Barry Diller. Soon afterward, Zuckerberg wrote on his Facebook page, “Is there a site that streams the World Cup final online? (I don’t own a TV.)”

Since late August, it’s also been pretty easy to track Zuckerberg through a new Facebook feature called Places, which allows users to mark their location at any time. At 2:45 A.M., E.S.T., on August 29th, he was at the Ace Hotel, in New York’s garment district. He was back at Facebook’s headquarters, in Palo Alto, by 7:08 P.M. On August 31st at 10:38 P.M., he and his girlfriend were eating dinner at Taqueria La Bamba, in Mountain View.

Zuckerberg may seem like an over-sharer in the age of over-sharing. But that’s kind of the point. Zuckerberg’s business model depends on our shifting notions of privacy, revelation, and sheer self-display. The more that people are willing to put online, the more money his site can make from advertisers. Happily for him, and the prospects of his eventual fortune, his business interests align perfectly with his personal philosophy. In the bio section of his page, Zuckerberg writes simply, “I’m trying to make the world a more open place.”

The world, it seems, is responding. The site is now the biggest social network in countries ranging from Indonesia to Colombia. Today, at least one out of every fourteen people in the world has a Facebook account. Zuckerberg, meanwhile, is becoming the boy king of Silicon Valley. If and when Facebook decides to go public, Zuckerberg will become one of the richest men on the planet, and one of the youngest billionaires. In the October issue of Vanity Fair, Zuckerberg is named No. 1 in the magazine’s power ranking of the New Establishment, just ahead of Steve Jobs, the leadership of Google, and Rupert Murdoch. The magazine declared him “our new Caesar.”

Despite his goal of global openness, however, Zuckerberg remains a wary and private person. He doesn’t like to speak to the press, and he does so rarely. He also doesn’t seem to enjoy the public appearances that are increasingly requested of him. Backstage at an event at the Computer History Museum, in Silicon Valley, this summer, one of his interlocutors turned to Zuckerberg, minutes before they were to appear onstage, and said, “You don’t like doing these kinds of events very much, do you?” Zuckerberg replied with a terse “No,” then took a sip from his water bottle and looked off into the distance.

This makes the current moment a particularly awkward one. Zuckerberg, or at least Hollywood’s unauthorized version of him, will soon be starring in a film titled “The Social Network,” directed by David Fincher and written by Aaron Sorkin. The movie, which opens the New York Film Festival and will be released on October 1st, will be the introduction that much of the world gets to Zuckerberg. Facebook profiles are always something of a performance: you choose the details you want to share and you choose whom you want to share with. Now Zuckerberg, who met with me for several in-person interviews this summer, is confronting something of the opposite: a public exposition of details that he didn’t choose. He does not plan to see the film.

Zuckerberg––or Zuck, as he is known to nearly everyone of his acquaintance––is pale and of medium build, with short, curly brown hair and blue eyes. He’s only around five feet eight, but he seems taller, because he stands with his chest out and his back straight, as if held up by a string. His standard attire is a gray T-shirt, bluejeans, and sneakers. His affect can be distant and disorienting, a strange mixture of shy and cocky. When he’s not interested in what someone is talking about, he’ll just look away and say, “Yeah, yeah.” Sometimes he pauses so long before he answers it’s as if he were ignoring the question altogether. The typical complaint about Zuckerberg is that he’s “a robot.” One of his closest friends told me, “He’s been overprogrammed.” Indeed, he sometimes talks like an Instant Message—brusque, flat as a dial tone—and he can come off as flip and condescending, as if he always knew something that you didn’t. But face to face he is often charming, and he’s becoming more comfortable onstage. At the Computer History Museum, he was uncommonly energetic, thoughtful, and introspective—relaxed, even. He addressed concerns about Facebook’s privacy settings by relaying a personal anecdote of the sort that his answers generally lack. (“If I could choose to share my mobile-phone number only with everyone on Facebook, I wouldn’t do it. But because I can do it with only my friends I do it.”) He was self-deprecating, too. Asked if he’s the same person in front of a crowd as he is with friends, Zuckerberg responded, “Yeah, same awkward person.”

Zuckerberg grew up in a hilltop house in Dobbs Ferry, New York. Attached to the basement is the dental office of his father, Edward Zuckerberg, known to his patients as “painless Dr. Z.” (“We cater to cowards,” his Web site reads.) There’s a hundred-and-sixty-gallon fish tank in the operating room, and the place is packed with marine-oriented tchotchkes that Dr. Zuckerberg’s patients have brought him. Mark’s mother, Karen, is a psychiatrist who stopped practicing to take care of the children and to work as her husband’s office manager.

Edward was an early user of digital radiography, and he introduced Atari BASIC computer programming to his son. The house and the dental office were full of computers. One afternoon in 1996, Edward declared that he wanted a better way of announcing a patient’s arrival than the receptionist yelling, “Patient here!” Mark built a software program that allowed the computers in the house and the office to send messages to one another. He called it ZuckNet, and it was basically a primitive version of AOL Instant Messenger, which came out the following year. The receptionist used it to ping Edward, and the kids used it to ping each other. One evening while Donna was working in her room, downstairs, a screen popped up: the computer contained a deadly virus and would blow up in thirty seconds. As the machine counted down, Donna ran up the stairs shouting, “Mark!”

Some kids played computer games. Mark created them. In all of our talks, the most animated Zuckerberg ever got—speaking with a big smile, almost tripping on his words, his eyes alert—was when he described his youthful adventures in coding. “I had a bunch of friends who were artists,” he said. “They’d come over, draw stuff, and I’d build a game out of it.” When he was about eleven, his parents hired a computer tutor, a software developer named David Newman, who came to the house once a week to work with Mark. “He was a prodigy,” Newman told me. “Sometimes it was tough to stay ahead of him.” (Newman lost track of Zuckerberg and was stunned when he learned during our interview that his former pupil had built Facebook.) Soon thereafter, Mark started taking a graduate computer course every Thursday night at nearby Mercy College. When his father dropped him off at the first class, the instructor looked at Edward and said, pointing to Mark, “You can’t bring him to the classroom with you.” Edward told the instructor that his son was the student.

Mark was not a stereotypical geek-klutz. At Exeter, he became captain of the fencing team. He earned a diploma in classics. But computers were always central. For his senior project at Exeter, he wrote software that he called Synapse. Created with a friend, Synapse was like an early version of Pandora—a program that used artificial intelligence to learn users’ listening habits. News of the software’s existence spread on technology blogs. Soon AOL and Microsoft made it known that they wanted to buy Synapse and recruit the teen-ager who’d invented it. He turned them down.

Zuckerberg decided, instead, to enter Harvard, in the fall of 2002. He arrived in Cambridge with a reputation as a programming prodigy. He sometimes wore a T-shirt with a little ape on it and the words “Code Monkey.” He joined the Jewish fraternity Alpha Epsilon Pi, and, at a Friday-night party there, Zuckerberg, then a sophomore, met his current girlfriend, Priscilla Chan, a Chinese-American from the Boston suburbs. They struck up a conversation while waiting in line for the bathroom. “He was this nerdy guy who was just a little bit out there,” Chan told me. “I remember he had these beer glasses that said ‘pound include beer dot H.’ It’s a tag for C++. It’s like college humor but with a nerdy, computer-science appeal.”

Zuckerberg had a knack for creating simple, addictive software. In his first week as a sophomore, he built CourseMatch, a program that enabled users to figure out which classes to take based on the choices of other students. Soon afterward, he came up with Facemash, where users looked at photographs of two people and clicked a button to note who they thought was hotter, a kind of sexual-playoff system. It was quickly shut down by the school’s administration. Afterward, three upperclassmen—an applied-math major from Queens, Divya Narendra, and twins from Greenwich, Connecticut, Cameron and Tyler Winklevoss—approached Zuckerberg for assistance with a site that they had been working on, called Harvard Connection.

Zuckerberg helped Narendra and the Winklevoss twins, but he soon abandoned their project in order to build his own site, which he eventually labelled Facebook. The site was an immediate hit, and, at the end of his sophomore year, Zuckerberg dropped out of Harvard to run it.

As he tells the story, the ideas behind the two social networks were totally different. Their site, he says, emphasized dating, while his emphasized networking. The way the Winklevoss twins tell it, Zuckerberg stole their idea and deliberately kept them from launching their site. Tall, wide-shouldered, and gregarious, the twins were champion rowers who competed in the Beijing Olympics; they recently earned M.B.A.s from Oxford. “He stole the moment, he stole the idea, and he stole the execution,” Cameron told me recently. The dispute has been in court almost since Facebook was launched, six years ago. Facebook eventually reached a settlement, reportedly worth sixty-five million dollars, with the Winklevosses and Narendra, but they are now appealing for more, claiming that Facebook misled them about the value of the stock they would receive.

To prepare for litigation against the Winklevosses and Narendra, Facebook’s legal team searched Zuckerberg’s computer and came across Instant Messages he sent while he was at Harvard. Although the IMs did not offer any evidence to support the claim of theft, according to sources who have seen many of the messages, the IMs portray Zuckerberg as backstabbing, conniving, and insensitive. A small group of lawyers and Facebook executives reviewed the messages, in a two-hour meeting in January, 2006, at the offices of Jim Breyer, the managing partner at the venture-capital firm Accel Partners, Facebook’s largest outside investor.

The technology site Silicon Alley Insider got hold of some of the messages and, this past spring, posted the transcript of a conversation between Zuckerberg and a friend, outlining how he was planning to deal with Harvard Connect:

FRIEND: so have you decided what you are going to do about the websites?
ZUCK: yea i’m going to fuck them
ZUCK: probably in the year
ZUCK: *ear

In another exchange leaked to Silicon Alley Insider, Zuckerberg explained to a friend that his control of Facebook gave him access to any information he wanted on any Harvard student:

ZUCK: yea so if you ever need info about anyone at harvard
ZUCK: just ask
ZUCK: i have over 4000 emails, pictures, addresses, sns
FRIEND: what!? how’d you manage that one?
ZUCK: people just submitted it
ZUCK: i don’t know why
ZUCK: they “trust me”
ZUCK: dumb fucks

According to two knowledgeable sources, there are more unpublished IMs that are just as embarrassing and damaging to Zuckerberg. But, in an interview, Breyer told me, “Based on everything I saw in 2006, and after having a great deal of time with Mark, my confidence in him as C.E.O. of Facebook was in no way shaken.” Breyer, who sits on Facebook’s board, added, “He is a brilliant individual who, like all of us, has made mistakes.” When I asked Zuckerberg about the IMs that have already been published online, and that I have also obtained and confirmed, he said that he “absolutely” regretted them. “If you’re going to go on to build a service that is influential and that a lot of people rely on, then you need to be mature, right?” he said. “I think I’ve grown and learned a lot.”

Zuckerberg’s sophomoric former self, he insists, shouldn’t define who he is now. But he knows that it does, and that, because of the upcoming release of “The Social Network,” it will surely continue to do so. The movie is a scathing portrait, and the image of an unsmiling, insecure, and sexed-up young man will be hard to overcome. Zuckerberg said, “I think a lot people will look at that stuff, you know, when I was nineteen, and say, ‘Oh, well, he was like that. . . . He must still be like that, right?’ ”

In Hollywood’s version, the early founding of Facebook is, as Sorkin said in an interview, “a classical story of friendship, loyalty, betrayal, and jealousy.” Sorkin described Zuckerberg as a “brilliant guy who’s socially awkward and who’s got his nose up against the window of social life. It would seem he badly wanted to get into one of these final clubs”—one of the exclusive, élite-within-élite party clubs at Harvard. The Winklevoss twins were members of the Porcellian Club, the most prestigious.

In the movie’s opening scene, according to a script that was leaked online, Zuckerberg and his girlfriend, Erica, a student at Boston University, sit in a campus bar, exchanging disparaging zingers. (“You don’t have to study,” he tells her. “How do you know I don’t have to study?” she asks. “Because you go to B.U.!”) Erica takes his hand, stares at him and says, “Listen. You’re going to be successful and rich. But you’re going to go through life thinking that girls don’t like you because you’re a tech geek. And I want you to know, from the bottom of my heart, that that won’t be true. It’ll be because you’re an asshole.”

The movie is based on “The Accidental Billionaires,” by Ben Mezrich, a book about the founding of Facebook. Mezrich is also the author of a best-seller, published in 2003, about college students striking it rich. The book, titled “Bringing Down the House,” used invented scenes, composite characters, and re-created dialogue. The new book has been criticized for using similar methods. Mezrich says that the book is not “an encyclopedic” description of Facebook’s founding but is nevertheless “a true story that Zuckerberg would rather not be told,” written in what he called a “thriller-esque style.” The book draws heavily on interviews that Mezrich conducted with Eduardo Saverin, Facebook’s initial business manager, who had a falling out with Zuckerberg and sued him. Mezrich did not talk to Zuckerberg. (The producer of “The Social Network,” Scott Rudin, tried to talk to Zuckerberg and other Facebook executives, but he was rebuffed.) Mezrich sold the movie rights to the book even before it was completed. He called Sorkin his “first reader,” and handed over chapters as soon as he finished them.

Sorkin said that creating Zuckerberg’s character was a challenge. He added that the college students were “the youngest people I’ve ever written about.” Sorkin, who is forty-nine, says that he knew very little about social networking, and he professes extreme dislike of the blogosphere and social media. “I’ve heard of Facebook, in the same way I’ve heard of a carburetor,” he told me. “But if I opened the hood of my car I wouldn’t know how to find it.” He called the film “The Social Network” ironically. Referring to Facebook’s creators, Sorkin said, “It’s a group of, in one way or another, socially dysfunctional people who created the world’s great social-networking site.”

Sorkin insisted that “the movie is not meant as an attack” on Zuckerberg. As he described it, however, Zuckerberg “spends the first one hour and fifty-five minutes as an antihero and the last five minutes as a tragic hero.” He added, “I don’t want to be unfair to this young man whom I don’t know, who’s never done anything to me, who doesn’t deserve a punch in the face. I honestly believe that I have not done that.”

As it happens, Sorkin’s “The West Wing” is one of Zuckerberg’s favorite television shows. He discovered it while on a trip to Spain with Chan, whom he has been dating, with a brief interruption, since 2003. In Madrid, they both got sick, and ended up watching the first season of the show in bed. In a Spanish department store, they bought DVDs of the six other seasons and eventually watched them all. Zuckerberg said that he liked the authenticity of the series—the way it captured the truth, at least as friends of his described it, of working in Washington.

I told Sorkin that his TV series was one of Zuckerberg’s favorites. He paused. “I wish you hadn’t told me that,” he said finally. When I asked Sorkin to guess the episode that Zuckerberg liked best, he said, “The Lemon-Lyman episode”—the one in Season Three where Josh Lyman, the deputy chief of staff, played by Bradley Whitford, discovers that he has a following on an online message board and unwisely interacts with its members.

Actually, Zuckerberg’s favorite episode, he told me, was “Two Cathedrals,” at the end of Season Two, in which Martin Sheen, who plays President Josiah Bartlet, grieves at the death of his longtime secretary and, after disclosing that he has multiple sclerosis, ponders whether he should seek reëlection. He is inside the National Cathedral and orders that it be temporarily sealed. He curses God in Latin and lights a cigarette. “It’s, like, even in journeys like Facebook, we’ve had some very serious ups and downs,” Zuckerberg said.

Zuckerberg says that many of the details he has read about the film are just wrong. (He had, for example, no interest in joining any of the final clubs.) When pressed about the movie and what it means for his public persona, he responded coolly: “I know the real story.”

A few days after we spoke, Zuckerberg changed his Facebook profile, removing “The West Wing” from his list of favorite TV shows.

On a recent Thursday afternoon, Zuckerberg took me for a stroll around the neighborhood in Palo Alto where he both lives and works. As he stepped out of the office and onto a street of expensive houses, he told me about his first trip to Silicon Valley. It was during winter break in January, 2004, a month before Facebook’s launch. He was nineteen. “I remember flying in, driving down 101 in a cab, and passing by all these tech companies like Yahoo!,” he said. His gray T-shirt was emblazoned with the word “hacker.” “I remember thinking, Maybe someday we’ll build a company. This probably isn’t it, but one day we will.”

We arrived at his house. Parked outside was a black Acura TSX, which he bought a couple of years ago, after asking a friend to suggest a car that would be “safe, comfortable, not ostentatious.” He drives a lot to relax and unwind, his friends say, and usually ends up at Chan’s apartment. She lives not far from Golden Gate Park and is a third-year medical student at the University of California, San Francisco. They spend most weekends together; they walk in the park, go rowing (he insists that they go in separate boats and race), play bocce or the board game the Settlers of Catan. Sundays are reserved for Asian cuisine. They usually take a two-week trip abroad in December. This year, they’re planning to visit China.

Zuckerberg has found all his homes on Craigslist. His first place was a sparse one-bedroom apartment that a friend described as something like a “crack den.” The next apartment was a two-bedroom, followed by his current place, a two-story, four-bedroom house that he told me is “too big.” He rents. (“He’s the poorest rich person I’ve ever seen in my life,” Tyler Winklevoss said.) As we crossed the driveway, we spotted Chan, sitting on a chair in the back yard, a yellow highlighter in her hand, reading a textbook; she plans to be a pediatrician. There was a hammock and a barbecue grill nearby. Surprised, Zuckerberg approached her and rubbed her right shoulder. “I didn’t know you were going to be here,” he said. She touched his right hand and smiled.

He walked into the house, which is painted in various shades of blue and beige, except for the kitchen, which is a vibrant yellow. Colors don’t matter much to Zuckerberg; a few years ago, he took an online test and realized that he was red-green color-blind. Blue is Facebook’s dominant color, because, as he said, “blue is the richest color for me—I can see all of blue.” Standing in his kitchen, leaning over the sink, he offered me a glass of water.

He returned the conversation to the winter of 2004, describing how he and his friends “would hang out and go together to Pinocchio’s, the local pizza place, and talk about trends in technology. We’d say, ‘Isn’t it obvious that everyone was going to be on the Internet? Isn’t it, like, inevitable that there would be a huge social network of people?’ It was something that we expected to happen. The thing that’s been really surprising about the evolution of Facebook is—I think then and I think now—that if we didn’t do this someone else would have done it.”

Zuckerberg, of course, did do it, and one of the reasons that he has held on to it is that money has never seemed to be his top priority. In 2005, MTV Networks considered buying Facebook for seventy-five million dollars. Yahoo! and Microsoft soon offered much more. Zuckerberg turned them all down. Terry Semel, the former C.E.O. of Yahoo!, who sought to buy Facebook for a billion dollars in 2006, told me, “I’d never met anyone—forget his age, twenty-two then or twenty-six now—I’d never met anyone who would walk away from a billion dollars. But he said, ‘It’s not about the price. This is my baby, and I want to keep running it, I want to keep growing it.’ I couldn’t believe it.”

Looking back, Chan said she thought that the time of the Yahoo! proposal was the most stressful of Zuckerberg’s life. “I remember we had a huge conversation over the Yahoo! deal,” she said. “We try to stick pretty close to what our goals are and what we believe and what we enjoy doing in life—just simple things,” she said.

Friends expect Chan and Zuckerberg to marry. In early September, Zuckerberg wrote on his Facebook page, “Priscilla Chan is moving in this weekend. Now we have 2x everything, so if you need any household appliances, dishes, glasses, etc please come by and take them before we give them away.”

Facebook’s headquarters is a two-story building at the end of a quiet, tree-lined street. Zuckerberg nicknamed it the Bunker. Facebook has grown so fast that this is the company’s fifth home in six years—the third in Palo Alto. There is virtually no indication outside of the Bunker’s tenant. Upon walking in, however, you are immediately greeted by what’s called the Facebook Wall, playing off the virtual chalkboards users have on their profiles. One day in early August, the Wall was covered with self-referential posts. An employee, addressing the constant criticism of the site’s privacy settings, had written, “How do I delete my post??? Why don’t you care about my privacy? Why is the default for this app everyone??” Inside is a giant sea of desks—no cubicles, no partitions, just open space with small conference rooms named after bands (Run-DMC, New Edition, ZZ Top) and bad ideas (Knife at a Gunfight, Subprime Mortgage, Beacon—a controversial advertising system that Facebook introduced in 2007 and then scrapped).

Zuckerberg’s desk is near the middle of the office, just a few steps away from his glass-walled conference room and within arm’s length of his most senior employees. Before arriving each morning, he works out with a personal trainer or studies Mandarin, which he is learning in preparation for the trip to China. Zuckerberg is involved in almost every new product and feature. His daily schedule is typically free from 2 P.M. to 6 P.M., and he spends that block of time meeting with engineers who are working on new projects. Debate is a hallmark of the meetings; at least a dozen of his employees pointed out, unprompted, what an “intense listener” Zuckerberg is. He is often one of the last people to leave the office. A photograph posted by a Facebook employee over Labor Day weekend showed Zuckerberg sitting at a long table in a conference room surrounded by other workers—all staring at their computers, coding away.

In the early years, Facebook tore through a series of senior executives. “A revolving door would be an understatement—it was very unstable,” Breyer said. Within ten days of hiring an executive, Breyer told me, Zuckerberg would e-mail or call him and say that the new hire needed to get the boot. Things calmed down in March, 2008, when Zuckerberg hired Sheryl Sandberg, a veteran of Google who was the chief of staff for Lawrence Summers when he was Secretary of the Treasury. She joined Facebook as the company’s chief operating officer, and executives followed her from companies like eBay, Genentech, and Mozilla. A flood of former Google employees soon arrived, too.

Meanwhile, however, most of Zuckerberg’s close friends, who worked for Facebook at the start, have left. Adam D’Angelo, who has been friends with Zuckerberg since their hacking and programming days at Exeter, teamed up with another former Facebook employee, Charlie Cheever, to start Quora.com, a social network that aggregates questions and answers on various topics. Chris Hughes, Zuckerberg’s Harvard roommate, left to join the Obama campaign and later founded the philanthropic site Jumo.com.

In part, the exodus reflects the status that former Facebook employees have in the tech world. But the departures also point to the difficulty some people have working for Zuckerberg. It’s hard to have a friend for a boss, especially someone who saw the site, from its inception, as “A Mark Zuckerberg production”—the tag line was posted on every page during Facebook’s early days. “Ultimately, it’s ‘the Mark show,’ ” one of his closest friends told me.

In late July, Facebook launched the beta version of Questions, a question-and-answer product that seems to be a direct competitor of Quora. To many people, the move seemed a vindictive attack on friends and former employees. In an interview, Cheever declined to comment, as did Matt Cohler, another friend who left the company, and who invested in Quora.

Chris Cox, Facebook’s vice-president of product, said that Facebook Questions is not an attack on Quora. “We’ve been talking about questions being the future of the way people search for stuff, so it was a matter of time before we built it,” Cox told me. “Getting there first is not what it’s all about.” He added, “What matters always is execution. Always.”

Zuckerberg’s ultimate goal is to create, and dominate, a different kind of Internet. Google and other search engines may index the Web, but, he says, “most of the information that we care about is things that are in our heads, right? And that’s not out there to be indexed, right?” Zuckerberg was in middle school when Google launched, and he seems to have a deep desire to build something that moves beyond it. “It’s like hardwired into us in a deeper way: you really want to know what’s going on with the people around you,” he said.

In 2007, Zuckerberg announced that Facebook would become a “platform,” meaning that outside developers could start creating applications that would run inside the site. It worked. The social-game company Zynga—the maker of FarmVille and Mafia Wars—is expected to earn more than five hundred million dollars this year, most of it generated from people playing on Facebook. In 2008, Zuckerberg unveiled Facebook Connect, allowing users to sign onto other Web sites, gaming systems, and mobile devices with their Facebook account, which serves as a digital passport of sorts. This past spring, Facebook introduced what Zuckerberg called the Open Graph. Users reading articles on CNN.com, for example, can see which articles their Facebook friends have read, shared, and liked. Eventually, the company hopes that users will read articles, visit restaurants, and watch movies based on what their Facebook friends have recommended, not, say, based on a page that Google’s algorithm sends them to. Zuckerberg imagines Facebook as, eventually, a layer underneath almost every electronic device. You’ll turn on your TV, and you’ll see that fourteen of your Facebook friends are watching “Entourage,” and that your parents taped “60 Minutes” for you. You’ll buy a brand-new phone, and you’ll just enter your credentials. All your friends—and perhaps directions to all the places you and they have visited recently—will be right there.

For this plan to work optimally, people have to be willing to give up more and more personal information to Facebook and its partners. Perhaps to accelerate the process, in December, 2009, Facebook made changes to its privacy policies. Unless you wrestled with a set of complicated settings, vastly more of your information—possibly including your name, your gender, your photograph, your list of friends—would be made public by default. The following month, Zuckerberg declared that privacy was an evolving “social norm.”

The backlash came swiftly. The American Civil Liberties Union and the Electronic Privacy Information Center cried foul. Users revolted, claiming that Facebook had violated the social compact upon which the company is based. What followed was a tug-of-war about what it means to be a private person with a public identity. In the spring, Zuckerberg announced a simplified version of the privacy settings.

I asked Zuckerberg about this during our walk in Palo Alto. Privacy, he told me, is the “third-rail issue” online. “A lot of people who are worried about privacy and those kinds of issues will take any minor misstep that we make and turn it into as big a deal as possible,” he said. He then excused himself as he typed on his iPhone 4, answering a text from his mother. “We realize that people will probably criticize us for this for a long time, but we just believe that this is the right thing to do.”

Zuckerberg’s critics argue that his interpretation and understanding of transparency and openness are simplistic, if not downright naïve. “If you are twenty-six years old, you’ve been a golden child, you’ve been wealthy all your life, you’ve been privileged all your life, you’ve been successful your whole life, of course you don’t think anybody would ever have anything to hide,” Anil Dash, a blogging pioneer who was the first employee of Six Apart, the maker of Movable Type, said. Danah Boyd, a social-media researcher at Microsoft Research New England, added, “This is a philosophical battle. Zuckerberg thinks the world would be a better place—and more honest, you’ll hear that word over and over again—if people were more open and transparent. My feeling is, it’s not worth the cost for a lot of individuals.”

Zuckerberg and I talked about this the first time I signed up for Facebook, in September, 2006. Users are asked to check a box to indicate whether they’re interested in men or in women. I told Zuckerberg that it took me a few hours to decide which box to check. If I said on Facebook that I’m a man interested in men, all my Facebook friends, including relatives, co-workers, sources—some of whom might not approve of homosexuality—would see it.

“So what did you end up doing?” Zuckerberg asked.

“I put men.”

“That’s interesting. No one has done a study on this, as far as I can tell, but I think Facebook might be the first place where a large number of people have come out,” he said. “We didn’t create that—society was generally ready for that.” He went on, “I think this is just part of the general trend that we talked about, about society being more open, and I think that’s good.”

Then I told Zuckerberg that, two weeks later, I removed the check, and left the boxes blank. A couple of relatives who were Facebook friends had asked about my sexuality and, at that time, at least, I didn’t want all my professional sources to know that I am gay.

“Is it still out?” Zuckerberg asked.

“Yeah, it’s still out.”

He responded with a flat “Huh,” dropped his shoulders, and stared at me, looking genuinely concerned and somewhat puzzled. Facebook had asked me to publish a personal detail that I was not ready to share.

In our last interview—this one over the phone—I asked Zuckerberg about “Ender’s Game,” the sci-fi book whose hero is a young computer wizard.

“Oh, it’s not a favorite book or anything like that,” Zuckerberg told me, sounding surprised. “I just added it because I liked it. I don’t think there’s any real significance to the fact that it’s listed there and other books aren’t. But there are definitely books—like the Aeneid—that I enjoyed reading a lot more.”

He first read the Aeneid while he was studying Latin in high school, and he recounted the story of Aeneas’s quest and his desire to build a city that, he said, quoting the text in English, “knows no boundaries in time and greatness.” Zuckerberg has always had a classical streak, his friends and family told me. (Sean Parker, a close friend of Zuckerberg, who served as Facebook’s president when the company was incorporated, said, “There’s a part of him that—it was present even when he was twenty, twenty-one—this kind of imperial tendency. He was really into Greek odysseys and all that stuff.”) At a product meeting a couple of years ago, Zuckerberg quoted some lines from the Aeneid.

On the phone, Zuckerberg tried to remember the Latin of particular verses. Later that night, he IM’d to tell me two phrases he remembered, giving me the Latin and then the English: “fortune favors the bold” and “a nation/empire without bound.”

Before I could point out how oddly applicable those lines might be to his current ambitions, he typed back:

again though
these are the most famous quotes in the aeneid
not anything particular that i found. ♦