His aggressive, ambitious demeanor won him a friend in Richard Nixon, but enemies in Congress. Various jobs in the Nixon administration led to his being appointed Ford's White House chief of staff. By all accounts, he ran a tight ship, distributing a manual called "Rumsfeld's Rules" to White House staff. Rule No. 1: Don't play president -- you're not.
Later, serving as secretary of defense under Ford, Rumsfeld was a hawk: He built up the military and opposed the SALT II strategic arms reduction treaty. But he improved the Pentagon's relations with Congress.
When Ford was defeated by Jimmy Carter in 1976, Rumsfeld headed for the corporate world after a brief flirtation with lecturing at Princeton, his alma mater. He became an expert at turning around troubled companies, starting at pharmaceutical firm G.D. Searle and later heading to electronics firm General Instrument, now part of Motorola. He's also served as a senior adviser to investment bank William Blair & Co. and as a director of various other firms.
But Rumsfeld has never been far from the presidency. He sought the vice-presidential nomination in 1980 and briefly ran for the Republican presidential nomination in 1988 against the elder George Bush, before dropping out and backing former Kansas Sen. Bob Dole for the job. He was also Dole's campaign chairman in his failed 1996 presidential bid against Bill Clinton.
Rumsfeld was called back into service in 1999 to head the nine-member Commission to Assess the Ballistic Missile Threat to the United States, a byproduct of wrangling between congressional Republicans and the Clinton administration over a missile defense system. His report supported the Republicans' contention that a missile defense was needed, and he blasted then-CIA Director George Tenet for increasing secrecy within the agency to such an extent that it was damaging the quality of intelligence provided to Congress.
He and his wife Joyce have been married 50 years. They have three children and five grandchildren.