Born in New York City, Oppenheimer earned a bachelor of arts degree in chemistry from Harvard University in 1925 and a doctorate in physics from the University of Göttingen in Germany in 1927, where he studied under Max Born. After research at other institutions, he joined the physics department at the University of California, Berkeley, where he became a full professor in 1936. He made significant contributions to theoretical physics, including achievements in quantum mechanics and nuclear physics such as the Born–Oppenheimer approximation for molecular wave functions, work on the theory of electrons and positrons, the Oppenheimer–Phillips process in nuclear fusion, and early work on quantum tunneling. With his students, he also made contributions to the theory of neutron stars and black holes, quantum field theory, and the interactions of cosmic rays.

In 1942, Oppenheimer was recruited to work on the Manhattan Project, and in 1943 he was appointed director of the project's Los Alamos Laboratory in New Mexico, tasked with developing the first nuclear weapons. His leadership and scientific expertise were instrumental in the project's success. On July 16, 1945, he was present at the first test of the atomic bomb, Trinity. In August 1945, the weapons were used against Japan in the bombings of Hiroshima and Nagasaki, the only use of nuclear weapons in an armed conflict.