Robert Fred Ellsworth (June 11, 1926 – May 9, 2011) was a United States' legislator and diplomat. He served as the United States Permanent Representative to NATO (an ambassadorial level appointment) between 1969 and 1971. He had previously served three terms as a Republican Member of Congress from Kansas, from 1961 to 1967, and as an Assistant to the President during the presidency of Richard Nixon; under President Gerald Ford, he was Deputy Secretary of Defense. Ellsworth also served as assistant to the chairman of the Federal Maritime Commission.
Ellsworth was born in Lawrence, Kansas, and was educated in the public schools of that city. He served in the United States Navy during World War II and the Korean War. In 1945, he was graduated with a baccalaureate in engineering from the University of Kansas, where he had been a member of the Alpha Nu chapter of the Beta Theta Pi collegiate fraternity. He then studied law at the University of Michigan Law School, from which he was graduated in 1949; he practiced law in Lawrence, Kansas, and in Springfield, Massachusetts.
The retired ambassador was admitted to the Order of Saint John as a knight of honor in 1995.
On November 9, 2010, Ellsworth provided commentary to KFMB regarding an unexplained missile launch off the coast of Los Angeles. He cautioned the news crew to wait for definitive answers from the military, then went on to speculate, "It could be a test firing of an intercontinental ballistic missile from a submarine, an underwater submarine, to demonstrate, mainly to Asia, that we could do that."