Harry S. Truman was a Missourian who served as President of the United States.
The Doctor once had a lively debate with Truman about Manhattan (referring to the "Manhattan Project") and the ethics of using fission weaponry on civilian populations. (PROSE: Falls the Shadow)
Because he was Franklin Delano Roosevelt's vice president, Truman became President of the United States when FDR died in office in 1945. He was elected in his own right three years later, surprising many who believed him a "caretaker" figure. He took part in the Potsdam Conference, negotiated the details of postwar Europe and authorised the use of nuclear bombs on Nagasaki and Hiroshima, Japan to end World War II. He also prosecuted the majority of the Korean War and fired General Douglas MacArthur for insubordination. He was widely regarded by those who knew him as "a tough little sonovabitch". (PROSE: Endgame)