He was picked to run Los Alamos not because he had a Nobel (he didn't) but because Groves needed someone who could hold the whole problem in his head at once. The Trinity detonation on July 16, 1945 produced 21 kilotons when they'd expected 0.3. Standing at the test site, he quoted the Bhagavad Gita: "Now I am become Death, the destroyer of worlds." That line stuck because it was the most honest thing anyone said about what they'd just done. He'd built the bomb. He'd also built the entire apparatus of American theoretical physics to build it with.
Post-war, he chaired the AEC's General Advisory Committee and loudly opposed the hydrogen bomb, which turned out to be career suicide. In 1954, Lewis Strauss orchestrated a security hearing where the prosecution had wiretapped his own defense team's conversations. The panel called him loyal but voted 2-1 against reinstating his clearance, citing "fundamental defects of character." He spent his last 13 years without a security clearance. The DOE finally vacated the 1954 decision in December 2022, 55 years after his death. The 2023 Nolan film grossed $975 million and won 7 Oscars, which is its own strange form of posthumous justice.
The "J" in his name isn't short for anything. He confirmed it to the U.S. Patent Office in 1946: just the letter J. He spoke six languages and learned Dutch in six weeks for a single lecture in the Netherlands. He named his New Mexico ranch "Perro Caliente," which translates to Hot Dog. He co-wrote a foundational black hole paper in 1939 with graduate student Hartland Snyder, then reportedly dropped the subject because he found it uninteresting.
A memorial at Princeton's Alexander Hall drew 600 people, including Hans Bethe, General Groves, and choreographer George Balanchine. His ashes were scattered off St. John in the U.S. Virgin Islands, where that beach is now called Oppenheimer Beach. The J. Robert Oppenheimer Memorial Committee was founded the same year and has held annual lectures in Los Alamos since 1971.