Donald Henry Rumsfeld was an American politician, government official and businessman who served as Secretary of Defense from 1975 to 1977 under president Gerald Ford, and again from 2001 to 2006 under President George W. Bush. He was both the youngest and the oldest secretary of defense. Additionally, Rumsfeld was a four-term U.S. Congressman from Illinois (1963–1969), director of the Office of Economic Opportunity (1969–1970), counselor to the president (1969–1973), the U.S. Representative to NATO (1973–1974), and the White House Chief of Staff (1974–1975). Between his terms as secretary of defense, he served as the CEO and chairman of several companies.

The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high-ranking member of the federal cabinet. The secretary of defense's position of command and authority over the military is second only to that of the president of the United States, who is the commander-in-chief. This position corresponds to what is generally known as a defense minister in many other countries. The secretary of defense is appointed by the president with the advice and consent of the Senate, and is by custom a member of the Cabinet and by law a member of the National Security Council.