Any transition, too, could be particularly challenging, as the reputations of Ms. Mayer and others who were hired early on are so closely intertwined with the company. “You get comfortable being wealthy, getting attention, living in the bubble,” Mr. Battelle said. “It will be interesting to watch at which point they declare ‘who am I?’ by their definition, not Google’s.”

PICKING at a salad in a conference room at Google’s headquarters here, Ms. Mayer says she is vexed by how some perceive her. “I am not a girl about town,” she says. “It isn’t how I project myself. It is how other people choose to project me.”

Perhaps. But it also happens to be true that she enjoys talking about herself. Last summer, in an interview with Yelp, a Web site that tracks restaurants and other local services, she gushed over her favorite dry cleaner and shoe repair shop, and where to find the best pineapple malts in Palo Alto (the Palo Alto Creamery).

She told Yelp that she didn’t like odd numbers, had researched how to get the best deal on a San Francisco hotel room using Priceline, and noted that her gay friends demanded invitations to her women-only “Sex and the City” movie screening and birthday party.

Despite her complaints, Ms. Mayer also seems relatively carefree about her privacy. While photographs of her and her fiancé, Zachary Bogue, a private-equity executive, are instant Internet fodder, she says she rarely turns down requests for her picture from Drew Altizer, a photographer she knows and often sees on the party circuit. “Drew is trying to pay me a compliment,” she says.

Whatever Ms. Mayer chooses to reveal about herself publicly, Craig Silverstein, Google’s director of technology and a close friend, says that none of it is self-serving.

“It is not her job in talking to Yelp to get people to know her,” he says. “Marissa doesn’t care about the chattering classes. She likes shopping, fashion. And she is not going to stop just because people don’t like that.”