Mike Mansfield, American politician and diplomat, 22nd United States Ambassador to Japan (d. 2001)
Michael Joseph Mansfield (March 16, 1903 – October 5, 2001) was an American politician and diplomat. A Democrat, he served as a US Representative (1943–1953) and a US Senator (1953–1977) from Montana. He was the longest-serving Senate Majority Leader and served from 1961 to 1977. During his tenure, he shepherded Great Society programs through the Senate.

Born in Brooklyn, Mansfield grew up in Great Falls, Montana. He lied about his age to serve in the United States Navy during World War I. After the war, he became a professor of history and political science at the University of Montana. He won election to the House of Representatives and served on the House Committee on Foreign Affairs during World War II.

In 1952, he defeated incumbent Republican Senator Zales Ecton to take a seat in the Senate. Mansfield served as Senate Majority Whip from 1957 to 1961. Mansfield ascended to Senate Majority Leader after Lyndon B. Johnson resigned from the Senate to become vice president. In the later years of the campaign, he eventually opposed escalation of the Vietnam War and supported President Richard Nixon's plans to replace US soldiers from Southeast Asia with Vietnamese belligerents.

After retiring from the Senate, Mansfield served as US Ambassador to Japan from 1977 to 1988. Upon retiring as ambassador, he was awarded the nation's highest civilian honor, the Presidential Medal of Freedom. Mansfield is the longest-serving American ambassador to Japan in history. After his ambassadorship, Mansfield served for a time as a senior adviser on East Asian affairs to Goldman Sachs, the Wall Street investment banking firm.