Fischer at Facebook's Menlo Park, Calif. headquarters
When Larry Summers asked Sheryl Sandberg, his up-and-coming special assistant at the Treasury Department, who else he should hire, she didn't hesitate. David Fischer was the best of the young staffers at the department, she said. That was in 1998. Since then Fischer has followed closely in the footsteps of his champion. After earning an MBA at Stanford, he became Sandberg's top deputy at Google, helping build a 4,000-employee ad operations group. When she left to become Facebook's COO, he first assumed her duties at Google and then joined her at Facebook in 2010. As vice president of business and marketing partnerships, the soft-spoken executive helped turn a nascent ad business into a $5 billion juggernaut. "He is incredibly efficient, and he is always the calmest person in the room," Sandberg tells Fortune.