Donald Rumsfeld served as the 13th Secretary of Defense from 1975 to 1977 under President Gerald Ford, and as the 21st Secretary of Defense from 2001 to 2006 under President George W. Bush. He is both the youngest and the oldest person to have served as Secretary of Defense. Rumsfeld was a four-term U.S. Congressman from Illinois (1962–1969), Director of the Office of Economic Opportunity (1969–1970), Counsellor to the President (1969–1973), the United States Permanent Representative to NATO (1973–1974), and White House Chief of Staff (1974–1975). His bestselling memoir, Known and Unknown, is now out in paperback.