Harry S. Truman(May 8, 1884 - December 26, 1972) was the 33rd President of the United States (1945-1953). As President Franklin D. Roosevelt's third vice-president and the 34th Vice President of the United States, he succeeded to the presidency on April 12, 1945, when President Roosevelt died less than three months after beginning his fourth term.

During World War I, Truman served as an artillery officer, making him the only president to have seen combat in World War I (his successor Eisenhower spent the war training tank crews in Pennsylvania). After the war he became part of the political machine of Tom Pendergast and was elected a county commissioner in Missouri and eventually a Democratic United States senator. After he gained national prominence as head of the wartime Truman Committee, Truman replaced vice president Henry A. Wallace as Roosevelt's running mate in 1944.

Truman faced challenge after challenge in domestic affairs. The disorderly postwar reconversion of the economy of the United States was marked by severe shortages, numerous strikes, and the passage of the TaftHartley Act over his veto. He confounded all predictions to win re-election in 1948, helped by his famous Whistle Stop Tour of rural America. After his re-election he was able to pass only one of the proposals in his Fair Deal program. He used executive orders to begin desegregation of the military and to create loyalty checks which dismissed thousands of communist supporters from office, even though he strongly opposed mandatory loyalty oaths for governmental employees, a stance that led to charges that his administration was soft on communism. Truman's presidency was also eventful in foreign affairs, with the end of World War II and his decision to use nuclear weapons against Japan, the founding of the United Nations, the Marshall Plan to rebuild Europe, the Truman Doctrine to contain communism, the beginning of the Cold War, the Berlin Airlift, the creation of the North Atlantic Treaty Organization (NATO), Chinese Civil War, and the Korean War. Corruption in Truman's administration, which was linked to certain members in the cabinet and senior White House staff, was a central issue in the 1952 presidential campaign and helped cause Adlai Stevenson, Truman's successor for the Democratic nomination for president, to lose to Republican Dwight D. Eisenhower in the 1952 presidential election.

Truman, whose demeanor was very different from that of the patrician Roosevelt, was a folksy, unassuming president. He popularized such phrases as "The buck stops here" and "If you can't stand the heat, you better get out of the kitchen." He overcame the low expectations of many political observers, who compared him unfavorably with his highly-regarded predecessor. At different times in his presidency, Truman earned both the lowest public approval ratings that had ever been recorded, and the highest to be recorded until 1991. Despite negative public opinion during his term in office, popular and scholarly assessments of his presidency became more positive after his retirement from politics and the publication of his memoirs. Truman's legendary upset victory in 1948 over Thomas E. Dewey is routinely invoked by underdog presidential candidates.