At ten o’clock on a weekday morning in August, Mark Zuckerberg, the chairman and C.E.O. of Facebook, opened the front door of his house in Palo Alto, California, wearing the tight smile of obligation. He does not enjoy interviews, especially after two years of ceaseless controversy. Having got his start as a programmer with a nocturnal bent, he is also not a morning person. Walking toward the kitchen, which has a long farmhouse table and cabinets painted forest green, he said, “I haven’t eaten breakfast yet. Have you?”

Since 2011, Zuckerberg has lived in a century-old white clapboard Craftsman in the Crescent Park neighborhood, an enclave of giant oaks and historic homes not far from Stanford University. The house, which cost seven million dollars, affords him a sense of sanctuary. It’s set back from the road, shielded by hedges, a wall, and mature trees. Guests enter through an arched wooden gate and follow a long gravel path to a front lawn with a saltwater pool in the center. The year after Zuckerberg bought the house, he and his longtime girlfriend, Priscilla Chan, held their wedding in the back yard, which encompasses gardens, a pond, and a shaded pavilion. Since then, they have had two children, and acquired a seven-hundred-acre estate in Hawaii, a ski retreat in Montana, and a four-story town house on Liberty Hill, in San Francisco. But the family’s full-time residence is here, a ten-minute drive from Facebook’s headquarters.

Occasionally, Zuckerberg records a Facebook video from the back yard or the dinner table, as is expected of a man who built his fortune exhorting employees to keep “pushing the world in the direction of making it a more open and transparent place.” But his appetite for personal openness is limited. Although Zuckerberg is the most famous entrepreneur of his generation, he remains elusive to everyone but a small circle of family and friends, and his efforts to protect his privacy inevitably attract attention. The local press has chronicled his feud with a developer who announced plans to build a mansion that would look into Zuckerberg’s master bedroom. After a legal fight, the developer gave up, and Zuckerberg spent forty-four million dollars to buy the houses surrounding his. Over the years, he has come to believe that he will always be the subject of criticism. “We’re not—pick your noncontroversial business—selling dog food, although I think that people who do that probably say there is controversy in that, too, but this is an inherently cultural thing,” he told me, of his business. “It’s at the intersection of technology and psychology, and it’s very personal.”

He carried a plate of banana bread and a carafe of water into the living room, and settled onto a navy-blue velvet sofa. Since co-founding Facebook, in 2004, his uniform has evolved from hoodies and flip-flops to his current outfit, a gray sweater, indigo jeans, and black Nikes. At thirty-four, Zuckerberg, who has very fair skin, a tall forehead, and large eyes, is leaner than when he first became a public figure, more than a decade ago. On the porch, next to the front door, he keeps a Peloton stationary bike, a favorite accessory in the tech world, which live-streams a personal trainer to your home. Zuckerberg uses the machine, but he does not love cycling. A few years ago, on his first attempt to use a road bike with racing pedals, he forgot to unclip, tipped over, and broke his arm. Except for cycling on his porch, he said, “I haven’t clipped in since.”

He and his wife prefer board games to television, and, within reach of the couch, I noticed a game called Ricochet Robots. “It gets extremely competitive,” Zuckerberg said. “We play with these friends, and one of them is a genius at this. Playing with him is just infuriating.” Dave Morin, a former Facebook employee who is the founder and C.E.O. of Sunrise Bio, a startup seeking cures for depression, used to play Risk with Zuckerberg at the office. “He’s not playing you in a game of Risk. He’s playing you in a game of games,” Morin told me. “The first game, he might amass all his armies on one property, and the next game he might spread them all over the place. He’s trying to figure out the psychological way to beat you in all the games.”

Across the tech industry, the depth of Zuckerberg’s desire to win is often remarked upon. Dick Costolo, the former C.E.O. of Twitter, told me, “He’s a ruthless execution machine, and if he has decided to come after you, you’re going to take a beating.” Reid Hoffman, the founder of LinkedIn, said, “There are a number of people in the Valley who have a perception of Mark that he’s really aggressive and competitive. I think some people are a little hesitant about him from that perspective.” Hoffman has been an investor in Facebook since its early days, but for a long time he sensed that Zuckerberg kept his distance because they were both building social networks. “For many years, it was, like, ‘Your LinkedIn thing is going to be crushed, so even though we’re friendly, I don’t want to get too close to you personally, because I’m going to crush you.’ Now, of course, that’s behind us and we’re good friends.”

When I asked Zuckerberg about this reputation, he framed the dynamic differently. The survival of any social-media business rests on “network effects,” in which the value of the network grows only by finding new users. As a result, he said, “there’s a natural zero-sumness. If we’re going to achieve what we want to, it’s not just about building the best features. It’s about building the best community.” He added, “I care about succeeding. And, yes, sometimes you have to beat someone to something, in order to get to the next thing. But that’s not primarily the way that I think I roll.”

For many years, Zuckerberg ended Facebook meetings with the half-joking exhortation “Domination!” Although he eventually stopped doing this (in European legal systems, “dominance” refers to corporate monopoly), his discomfort with losing is undimmed. A few years ago, he played Scrabble on a corporate jet with a friend’s daughter, who was in high school at the time. She won. Before they played a second game, he wrote a simple computer program that would look up his letters in the dictionary so that he could choose from all possible words. Zuckerberg’s program had a narrow lead when the flight landed. The girl told me, “During the game in which I was playing the program, everyone around us was taking sides: Team Human and Team Machine.”

If Facebook were a country, it would have the largest population on earth. More than 2.2 billion people, about a third of humanity, log in at least once a month. That user base has no precedent in the history of American enterprise. Fourteen years after it was founded, in Zuckerberg’s dorm room, Facebook has as many adherents as Christianity.

A couple of years ago, the company was still revelling in its power. By collecting vast quantities of information about its users, it allows advertisers to target people with precision—a business model that earns Facebook more ad revenue in a year than all American newspapers combined. Zuckerberg was spending much of his time conferring with heads of state and unveiling plans of fantastical ambition, such as building giant drones that would beam free Internet (including Facebook) into developing countries. He enjoyed extraordinary control over his company; in addition to his positions as chairman and C.E.O., he controlled about sixty per cent of shareholder votes, thanks to a special class of stock with ten times the power of ordinary shares. His personal fortune had grown to more than sixty billion dollars. Facebook was one of four companies (along with Google, Amazon, and Apple) that dominated the Internet; the combined value of their stock is larger than the G.D.P. of France.

“Best of all, he has this wonderful passion for life that he doesn’t expect me to share.” Facebook

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For years, Facebook had heard concerns about its use of private data and its ability to shape people’s behavior. The company’s troubles came to a head during the Presidential election of 2016, when propagandists used the site to spread misinformation that helped turn society against itself. Some of the culprits were profiteers who gamed Facebook’s automated systems with toxic political clickbait known as “fake news.” In a prime example, at least a hundred Web sites were traced to Veles, Macedonia, a small city where entrepreneurs, some still in high school, discovered that posting fabrications to pro-Donald Trump Facebook groups unleashed geysers of traffic. Fake-news sources also paid Facebook to “microtarget” ads at users who had proved susceptible in the past.