Harry S. Truman (May 8, 1884 – December 26, 1972) was the 33rd President of the United States, from 1945 to 1953. He became president when President Franklin D. Roosevelt died in office.
As president, Truman made important foreign policy decisions, such as using atomic weapons on Japan to end World War II, repairing Europe (which was destroyed during the war), beginning the Cold War, and getting the U.S. involved in the Korean War.
Early years

Truman was raised in Independence, Missouri. He lived for 12 years as a Missouri farmer.
Political life
Truman was active in the Democratic Party. In 1922, he was elected judge of Jackson County Court.
In 1934, Truman was elected Senator of Missouri.
Truman became the head of a committee that looked at how much money the United States was spending on defense during World War II. He found billions of dollars of spending that he thought was a waste and could be cut out of what the U.S. was spending.
In 1944, President Roosevelt ran for re-election again with Truman as his vice president.

They won the election, and Roosevelt began his fourth term as president. On April 12, 1945, shortly after his fourth inauguration, Franklin Delano Roosevelt died. Truman became president right toward the end of WWII.
Presidency

Nazi Germany surrendered less than a month after Truman became president. This ended the war in Europe. However, the Japanese kept fighting. The United States made the Potsdam Declaration, telling Japan to surrender or it would face “prompt and utter destruction.” Japan did not surrender. As a result, Truman ordered the first atomic bomb to be dropped on Hiroshima, Japan, on August 6th, 1945. Three days later, Truman ordered the second atomic bomb to be dropped on Nagasaki, Japan. Japan surrendered and the war ended.
After the war

After the war, Truman ordered Europe (which was destroyed during the war) to be repaired with the Marshall Plan. Truman ordered the Berlin Airlift, which flew in tons of food to West Germany to feed the starving people.
Truman also helped create the United Nations, an organization which was based on the League of Nations. The United Nations still exists today. Its goal is for different countries to work together to help humanity and to promote peace.
Truman sent Congress his “Fair Deal.” It was based on Roosevelt’s New Deal. It gave more money to education, more money to farmers, and a higher minimum wage for workers. Labor union leaders asked him for higher wages and more benefits.
In 1948, Truman ran for a second term as President against Thomas Dewey. He was the underdog and everyone thought he was going to lose. The Chicago Tribune published a newspaper on the night of the election with the title “Dewey Defeats Truman”. To everyone’s surprise, Harry Truman won the election.

The Korean War
On June 25, 1950, North Korea attacked South Korea. China supported North Korea. North Korea wanted to bring Communism into South Korea. The U.S. supported South Korea and joined the war 2 days later.
During the end of his term, Harry Truman’s approval rating was at an all-time low. He was very unpopular because thousands of Americans died in the Korean War, and people were accusing many of Truman’s employees of being communists. His second term as president ended on January 20, 1953. The Korean War ended about six months later.
As time passed, Truman’s reputation got better. Many historians now believe that Harry Truman was a great president.

(edited from – source)