Mulligan joined the insurer as executive vice president in 2008, then quickly got promoted twice before moving into the CEO spot in July, making her one of 15 women to lead a Fortune 500 company. The fourth-largest mutual life insurer in the U.S. manages $33 billion in assets.
Boardroom battles and power plays shaped this year's U.S. list, which boasts eight new faces and -- surprise! -- a new No. 1.
