Three degrees of Reid Hoffman

FORTUNE -- One day last fall, Reid Hoffman, the social networking guru and founder of LinkedIn (LNKD), woke up at the MGM Grand in Las Vegas, where he breakfasted with Magic Johnson and then spoke to a few hundred HR professionals. On a flight to San Francisco he scarfed down a turkey sandwich while I quizzed him, then sat for the closing interview at the Web 2.0 Summit. While catching up with friends in the greenroom, he took a call from a board member. Next: dinner with Microsoft (MSFT, Fortune 500) CEO Steve Ballmer and guests before -- finally -- retiring to his Palo Alto home. This, says Hoffman, is pretty much a normal day. "I don't know what the opposite of a sociopath is," says his close friend, investor and PayPal veteran Peter Thiel, "but he is that."

Hoffman, 44, is a polymath with degrees from Stanford (symbolic systems) and Oxford (philosophy). But he owes his success to his ability to navigate the ever-expanding group of people he calls his tribe. His MO is making time for people because their ideas are interesting rather than potentially profitable; he is quick to offer favors for friends. In 2007, when Bret Taylor launched Friendfeed, the company he sold to Facebook, Hoffman offered him detailed feedback on his product strategy. "He sets an example for how entrepreneurs should help each other," says Taylor, now Facebook's CTO.

Hoffman's ability to both grasp technology changes and connect on a deeply human level has made him one of Web 2.0's biggest winners. He started the very first social networking website, Socialnet.com, back in 1997 when Mark Zuckerberg was still in middle school. He later helped broker Facebook's first $500,000 investment (kicking in $40,000 of his own). He founded LinkedIn when the idea of sharing your little black book was career suicide; now it has 135 million users. And he has had a hand in nearly every other big Web 2.0 company, including Friendster, Digg, and Zynga (ZNGA).

In 2009, Hoffman joined venture firm Greylock, where he runs a seed fund and helps manage a portfolio of nearly 100 companies, including Groupon (GRPN), Tumblr, and AirBnb. With LinkedIn's IPO and other investments, Hoffman is worth some $1.5 billion. Now comes his book, The Start-Up of You, in which he shares tips on building a great career. Paramount among them: being an authentic networker. After all, Hoffman has 800 Facebook friends and 2,579 LinkedIn connections, and sits on six corporate and four nonprofit boards. At meetings he spreads out no fewer than five screens -- iPads, Androids -- to keep up with contacts. That skill has helped Hoffman recruit to Greylock such web stars as former Mozilla CEO John Lilly. Hoffman now believes that the defining principle of the web's next innovation cycle is data. "We are generating a massive amount," he says. "What are we inventing?" It's one of the first questions he asks everyone he meets. The other: "How can I help you?

This article is from the February 6, 2012 issue of Fortune.