Unlike many of his corporate peers, he has become an outspoken supporter of healthcare reform – though Mr Williams, 58, is careful not to endorse the specific plan of any candidate or political party.

Formerly president of Blue Cross of California, Chicago-born Mr Williams joined Aetna as chief operating officer in 2001, when the company was in financial trouble. Part of the management team that turned Aetna around, he became chief executive two years ago.

A reserved, self-confessed technology geek in an industry that has often prized leaders with a medical background, Mr Williams is a champion of using IT to make healthcare cheaper and more transparent. He was recently a member of a group of executives convened by Barack Obama, the Democratic Party's presidential candidate, to talk about business and the economy.