“When Ed Whitacre decides, it’s not negotiable. If he decides against you, you’re done.”

–Coca-Cola exec Wendy Clark, about General Motors’ new CEO, whom she worked for when he headed AT&T . Today, the GM board ousted CEO Fritz Henderson, who was in the post just eight months, and installed Whitacre, GM’s chairman, as the new chief executive.

No doubt, Whitacre had a key role in the power shift.

And hearing Clark talk about the man, you understand that anyone working under him is on a short leash. Clark, a rising star who is SVP of Integrated Marketing and Communications at Coke and previously headed marketing for Whitacre at AT&T, spoke about his unusual leadership style last month at a Fortune Most Powerful Women dinner event in Atlanta. “He doesn’t talk much. He listens intently. He surrounds himself with experts who know everything,” Clark said. She calls Whitacre “the greatest mentor” she’s ever had.

Her view of Whitacre at GM? “If Ed can’t fix it, no one can fix it,” she says.–Patricia Sellers