President Harry S. Truman, the 33rd President of the United States, is known for several key achievements and events during his presidency from 1945 to 1953. He made the decision to use atomic bombs on Japan to end World War II, initiated the Marshall Plan to aid European recovery, and established the Truman Doctrine to contain communism. He also oversaw the creation of NATO and addressed civil rights issues, including desegregating the military. His leadership during the early Cold War era significantly shaped U.S. foreign policy.

It seems there might be a mix-up in the question. Truman and Oppenheimer are not characters in the same movie. "The Truman Show," featuring Jim Carrey as Truman Burbank, is a film about a man living in a constructed reality, while "Oppenheimer," directed by Christopher Nolan, focuses on J. Robert Oppenheimer and the development of the atomic bomb. If you meant a specific interaction or theme, please clarify, and I'll be happy to help!

Truman was not assassinated in the film "The Truman Show." The movie, released in 1998, follows Truman Burbank, a man who discovers that his entire life is a televised reality show. The plot revolves around his quest for truth and freedom, rather than an assassination. If you meant a different movie or context, please clarify, and I'll be happy to help!

Harry S. Truman stopped being president after completing his second term on January 20, 1953. He chose not to run for re-election in 1952 due to low approval ratings, the Korean War, and the political climate of the time. The 22nd Amendment, ratified in 1951, also limited presidents to two terms, but Truman was not bound by it since he took office before it was passed. After leaving office, he returned to private life in Missouri.