The atomic bomb was invented as part of the Manhattan Project during World War II, led by American theoretical physicist J. Robert Oppenheimer, who is often called the "father of the atomic bomb." Oppenheimer directed the Los Alamos Laboratory where the bomb was designed and developed. The project involved many prominent scientists, including Leo Szilard and Hans Bethe, who contributed foundational research on nuclear fission and chain reactions enabling the bomb's creation. The first successful nuclear weapon was built in 1945 and used in the war shortly thereafter.