As chief executive, Mr. Zuckerberg has proved himself a savvy negotiator of deals.

“Mark will convince companies he is going to acquire that they should accept a deal on a projected valuation,” says one C.E.O. who held talks with Mr. Zuckerberg. “Then, he’ll go back to investors who want to put money into Facebook and say, look, this start-up was going to join us at this valuation, so you should invest at that number.”

For example, during the closing hours of the Instagram talks, Mr. Zuckerberg and Kevin Systrom, the Instagram chief executive, reached a deal in private, at Mr. Zuckerberg’s $7 million, five-bedroom home in Palo Alto, while their lawyers and advisers watched from afar.

“As the deal came to a close, Mark and Kevin sat outside and ate steaks and ice cream, while the lawyers all sat inside watching ‘Game of Thrones,’ ” said a person who was present. It wasn’t lost on those there, this person said, that “two 20-somethings were alone hammering out the terms of the deal.”

The Instagram deal underscored how Mr. Zuckerberg has cemented his power over the last eight years. Facebook’s board, which got a brief e-mail about the deal a few days before it was announced, according to those close to the company, never pushed back.

And so now, as C.E.O., Mark Zuckerberg has never been more secure — or, given the coming I.P.O., more exposed. By most accounts, he has few close friends outside the company. He has a girlfriend, Priscilla Chan, and a dog, Beast. Like his master, Beast, a Puli with thick dreadlocks, has a page on Facebook. (It has 541,786 “likes.”)

On some evenings, as dusk falls in Menlo Park, Mr. Zuckerberg and a small circle of his lieutenants play roller hockey, and maybe knock back a beer or two, outside Facebook’s headquarters. The game is a relatively recent arrival there, although Mr. Zuckerberg has played it since his boyhood in Dobbs Ferry.

Out in the courtyard, the crew — almost all of them men, almost all in their 20s — hoot and skate until it is almost too dark to see much of anything. Across the courtyard floor, giant black tiles spell out the word “hack.” They’ve nicknamed their rink “Hack Stadium.”

The Facebook boys and their captain, Mark Zuckerberg, skate hard. They line up shots with care. And they play to win.