Harry S. Truman (May 8, 1884 – December 26, 1972) was the 33rd president of the United States, serving from 1945 to 1953. As the 34th vice president in 1945, he assumed the presidency upon the death of Franklin D. Roosevelt that year. Subsequently, Truman implemented the Marshall Plan in the aftermath of World War II to rebuild the economy of Western Europe, and established both the Truman Doctrine and NATO to contain the expansion of Soviet communism. A member of the Democratic Party, he proposed numerous New Deal coalition liberal domestic reforms, but few were enacted by the conservative coalition that dominated the United States Congress.

Born in Lamar, Missouri, Truman was raised in Independence, Missouri, and during World War I fought in France as a captain in the Field Artillery. Returning home, he opened a haberdashery in Kansas City, Missouri, and was elected as a judge of Jackson County in 1922. Truman was elected to the U.S. Senate for Missouri in 1934. Between 1940 and 1944, he gained national prominence as the chairman of the Truman Committee, which aimed to reduce waste and inefficiency in wartime contracts. Truman was elected vice president in the 1944 presidential election and became president upon Roosevelt's death in April 1945. Only then was he told about the ongoing Manhattan Project and the atomic bomb. Truman authorized the first and only use of nuclear weapons in war against the Japanese cities of Hiroshima and Nagasaki.

Truman's administration engaged in an internationalist foreign policy by working closely with Britain. Truman staunchly denounced isolationism. He energized the New Deal coalition during the 1948 presidential election, despite a divided Democratic Party, and won a surprise victory against the Republican Party's nominee, Thomas E. Dewey. Truman presided over the onset of the Cold War in 1947. He oversaw the Berlin Airlift and the Marshall Plan in 1948. With America's involvement in the Korean War (1950–1953), South Korea repelled the invasion by North Korea. Domestically, the postwar economic challenges such as strikes and inflation created a mixed reaction over the effectiveness of his administration. In 1948, he proposed that Congress should pass comprehensive civil rights legislation. Congress refused, so Truman issued Executive Order 9980 and Executive Order 9981, which prohibited discrimination in agencies of the federal government and desegregated the United States Armed Forces.

Investigations revealed corruption in parts of the Truman administration, and this became a major campaign issue in the 1952 presidential election, although they did not implicate Truman himself. He was eligible for reelection in 1952 but he chose not to run due to poor polling. Subsequently, Truman went into a retirement marked by the founding of his presidential library and the publication of his memoirs. It was long believed that Truman's retirement years were financially difficult, resulting in Congress establishing a pension for former presidents. However, evidence eventually emerged that he amassed considerable wealth, some of it during his presidency. When Truman left office, his administration was heavily criticized. Despite this controversy, scholars rank Truman in the first quartile of U.S. presidents. In addition, critical reassessments of his presidency have improved his reputation among historians and the general population.

Harry S. Truman was born in Lamar, Missouri, on May 8, 1884, the oldest child of John Anderson Truman and Martha Ellen Young Truman. He was named for his maternal uncle, Harrison "Harry" Young. His middle initial, "S", is not an abbreviation of one particular name. Rather, it honors both his grandfathers, Anderson Shipp Truman and Solomon Young, a somewhat common practice in the American South at the time. A brother, John Vivian, was born soon after Harry, followed by sister Mary Jane. While Truman's ancestry was primarily English, he also had some Scots-Irish, German, and French ancestry.

John Truman was a farmer and livestock dealer. The family lived in Lamar until Harry was ten months old, when they moved to a farm near Harrisonville, Missouri. They next moved to Belton and in 1887 to his grandparents' 600-acre (240 ha) farm in Grandview. When Truman was six, his parents moved to Independence, Missouri, so he could attend the Presbyterian Church Sunday School. He did not attend a conventional school until he was eight years old. While living in Independence, he served as a Shabbos goy for Jewish neighbors, doing tasks for them on Shabbat that their religion prevented them from doing on that day.

Truman was interested in music, reading, history, and math, all encouraged by his mother, with whom he was very close. As president, he solicited political as well as personal advice from her. Truman learned to play the piano at age seven and took lessons from Mrs. E.C. White, a well-respected teacher in Kansas City. He got up at five o'clock every morning to practice the piano, which he studied more than twice a week until he was fifteen, becoming quite a skilled player. Truman worked as a page at the 1900 Democratic National Convention in Kansas City; his father had many friends active in the Democratic Party who helped young Harry to gain his first political position.

After graduating from Independence High School in 1901, Truman took classes at Spalding's Commercial College, a Kansas City business school. He studied bookkeeping, shorthand, and typing but stopped after a year.