NEW YORK — Before 2010, Mark Zuckerberg, the 26-year-old co-founder and CEO of Facebook, was primarily known as a mysterious, sweatshirted figure, a Silicon Valley wunderkind familiar mainly to those in tech circles.

But this year, Zuckerberg has been thrust into pop culture ubiquity, appearing on screens of all shapes and sizes, from "Oprah" to one of the year’s most acclaimed films.

On Wednesday, his public ascent was solidified by Time magazine, which named him its "Person of the Year." He’s the youngest choice for the honor since the first one chosen, Charles Lindbergh in 1927.

In a posting — where else? — on his Facebook page, Zuckerberg said being named Time’s "Person of the Year" was "a real honor and recognition of how our little team is building something that hundreds of millions of people want to use to make the world more open and connected. I’m happy to be a part of that."

It caps a remarkable year for Zuckerberg and Facebook, which has more than 500 million users worldwide and market valuations that go into double-digit billions. In countless redesigns and new features, Facebook has been pushing toward becoming not just a social media hangout, but also the underlying, connecting fabric of the Internet.

Time, which many expected to choose the news-making WikiLeaks founder Julian Assange for "Person of the Year," cited Zuckerberg "for changing how we all live our lives."

"I’m trying to make the world a more open place," Zuckerberg says in the "bio" line of his own Facebook page.

Zuckerberg was perhaps prompted to expand his public persona because others were doing it for him. "The Social Network," David Fincher and Aaron Sorkin’s acclaimed drama of the contentious creation of Facebook, has supplied a narrative that in some ways is unkind to Zuckerberg and Facebook.

The film depicts Zuckerberg (played by Jesse Eisenberg) as a brilliant, power-hungry, back-stabbing hacker motivated by social acceptance and girls. Facebook has called the film (which Sorkin wrote based partly on Ben Mezrich’s book "The Accidental Billionaires" and without Zuckerberg’s cooperation) "fiction."

But that hasn’t stopped it from becoming a sensation with critics and moviegoers, and arguably the most talked-about film of the year. It has established itself as an Oscar front-runner.

The New York Film Critics Circle, the Los Angeles Film Critics Association and the National Board of Review have all picked "The Social Network" as the best film of the year. On Tuesday, it received six Golden Globe nominations, including best picture, drama, going up against its chief rival, the British monarchy tale "The King’s Speech," which led with seven nominations.

Zuckerberg countered the release of the film with a $100 million donation over five years to the Newark, N.J., school system. He appeared on "The Oprah Winfrey Show" to announce the donation. He’s in the company of media titans Carl Icahn, Barry Diller and others who have joined Giving Pledge, an effort led by Microsoft founder Bill Gates and investor Warren Buffett to commit the country’s wealthiest people to step up their charitable donations.

Ahead of the release of "The Social Network," Sorkin defended the movie’s veracity.

"I have to believe that their PR people are every bit as good as our PR people, and they’ve decided just to say ‘fiction’ as often as they can," Sorkin said. "They have not identified yet anything in the movie that’s been fictionalized. They’ve nibbled around the edges a little bit that he was drinking a Manhattan when he was really drinking a martini, and that kind of thing. But they’re not going to be able to. The movie’s true."

Fincher, for his part, professed sympathy for Zuckerberg, and said he understood the pressure of being a young talent with little patience for those less intelligent. He said accuracy was important, but that it was worth remembering the stakes: "You’re talking about people who had their feelings hurt."

For Zuckerberg, though, the film turned out to be less something to fear than to scoff at. He even took the whole company to see "The Social Network," buying out two theaters for the occasion.

"It’s pretty interesting to see what parts they got right and what parts they got wrong," Zuckerberg said earlier this month in a "60 Minutes" interview. "They got every single T-shirt that they had the Mark Zuckerberg character wearing right. I think I actually own those T-shirts.

"But I mean, there are hugely basic things that they got wrong, too. I mean, they made it seem like my whole motivation for building Facebook was so I could get girls, right? And they completely left out the fact that my girlfriend, I’ve been dating since before I started Facebook, right?"

The film is sure to remain a hot topic until the Feb. 27 Academy Awards.

"It’s a movie for its time," said Kevin Spacey, a producer of the film. "And yet I think it’s a movie that’s going to last."

But Facebook touches the lives of an enormous audience unimaginable to any Hollywood film. Zuckerberg, who grew up in the New York City suburb of Dobbs Ferry, the son of a computer-obsessed dentist, has built Facebook from a dorm room creation at Harvard into the largest social networking site in the world.

As it grew, he steadily turned down offers from companies like Yahoo and Microsoft, and has so far declined to take Facebook public. Asked about a Facebook IPO on "60 Minutes," Zuckerberg said, "Maybe."

"A lot of people who I think build startups or companies think that selling the company or going public is this endpoint," he said. "It’s like you win when you go public. And that’s just not how I see it."

Not everyone sees Facebook’s rise as a good thing. Some question the depth of its social interaction, and many have raised questions over its attitudes about privacy. Facebook has continually urged its users to share more personal information, often prompting criticism from privacy groups and users.

But Zuckerberg, now a celebrity himself and one of the world’s youngest billionaires, sees Facebook as a universal identity system that could challenge Google and even e-mail for the basis of Internet communication. In his book "The Facebook Effect," David Kirkpatrick wrote that Zuckerberg is less motivated by money than his vision for the Web and Facebook.

"The question I ask myself like almost every day is: ‘Am I doing the most important thing I could be doing?’" Zuckerberg told him. "Unless I feel like I’m working on the most important problem that I can help with, then I’m not going to feel good about how I’m spending my time. And that’s what this company is."

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On the Net: www.time.com/