A name you probably recognize from your history books, Harry Truman is better known as the thirty-third President of the United States and the person who ultimately decided to use atomic bombs to end World War II.
Before that, though, he was a senator from Missouri who didn't like how much money was being funneled into a top-top-secret project that no one was allowed to know about. After he made himself a royal pain in the buttinsky for those who were trying to keep the Manhattan Project a secret, he was surprisingly selected by Roosevelt as his running mate in the 1944 election. He quickly discovered that FDR had wanted him to win votes, not really to help run the country, but all of that changed traumatically when Roosevelt died suddenly in April of 1945.
After he was sworn in, Truman was briefed about everything that was happening with the progress of building an atomic bomb, and he felt blindsided by the sudden thrust into power.
"If you ever pray, pray for me now," Truman told reporters when they surrounded him the following day. "I don't know whether you fellows ever had a load of hay fall on you, but when they told me yesterday what had happened, I felt like the moon, the stars, and all the planets had fallen on me." (Falling Stars.(28).20)
According to Sheinkin, Truman struggled to assert his own presidential identity while trying to maintain Roosevelt's popular policies, which at times were contradictory. Above all, though, it seems like Truman, while trying to adhere to his own strong sense of morality, would often succumb to political pressures rather than ethical ones.
After successfully using atomic bombs to end the war, Truman became a major proponent of nuclear proliferation. Despite objections from some of the world's greatest minds (Oppenheimer and Einstein, to name, uh, two really smart dudes), he wanted more bombs, and bigger bombs, in order to continue America's ability to intimidate other nations into submission.