Oppenheimer is a 2023 epic biographical thriller film written, co-produced, and directed by Christopher Nolan. It follows the life of J. Robert Oppenheimer, the American theoretical physicist who helped develop the first nuclear weapons during World War II. Based on the 2005 biography American Prometheus by Kai Bird and Martin J. Sherwin, the film dramatizes Oppenheimer's studies, his direction of the Los Alamos Laboratory and his 1954 security hearing. Cillian Murphy stars as Oppenheimer, alongside Robert Downey Jr. as the United States Atomic Energy Commission member Lewis Strauss. The ensemble supporting cast includes Emily Blunt, Matt Damon, Florence Pugh, Josh Hartnett, Casey Affleck, Rami Malek, and Kenneth Branagh.

Oppenheimer was announced in September 2021. It was Nolan's first film not distributed by Warner Bros. Pictures since Memento (2000), due to his conflicts regarding the studio's simultaneous theatrical and HBO Max release schedule. Murphy was the first cast member to join, with the rest joining between November 2021 and April 2022. Pre-production began by January 2022, and filming took place from February to May. The cinematographer, Hoyte van Hoytema, used a combination of IMAX 65 mm and 65 mm large-format film, including, for the first time, selected scenes in IMAX black-and-white film photography. As with many of his previous films, Nolan used extensive practical effects, with minimal compositing.

Oppenheimer premiered at Le Grand Rex in Paris on July 11, 2023, and was theatrically released in the United States and the United Kingdom on July 21 by Universal Pictures. Its concurrent release with Warner Bros.'s Barbie was the catalyst of the "Barbenheimer" phenomenon, encouraging audiences to see both films as a double feature. Oppenheimer received critical acclaim and grossed $975 million worldwide, becoming the third-highest-grossing film of 2023, the highest-grossing World War II–related film, the highest-grossing biographical film and the second-highest-grossing R-rated film of all time at the time of its release.

The recipient of many accolades, Oppenheimer was nominated for thirteen awards at the 96th Academy Awards and won seven, including Best Picture, Best Director (Nolan), Best Actor (Murphy), and Best Supporting Actor (Downey). It also won five Golden Globe Awards (including Best Motion Picture – Drama) and seven British Academy Film Awards (including Best Film), and was named one of the top 10 films of 2023 by the National Board of Review and the American Film Institute.

In 1926, 22-year-old doctoral student J. Robert Oppenheimer grapples with anxiety and homesickness while studying experimental quantum physics under Patrick Blackett at the University of Cambridge in England. Oppenheimer clashes with Blackett, leaving him a poisoned apple, but he later retrieves it. Visiting scientist Niels Bohr advises Oppenheimer to study theoretical physics at the University of Göttingen in Germany.

Oppenheimer completes his PhD and meets scientist Isidor Isaac Rabi. They later meet theoretical physicist Werner Heisenberg in Switzerland. Wanting to expand quantum physics research in the United States, Oppenheimer teaches at the University of California, Berkeley and the California Institute of Technology. He marries Katherine "Kitty" Puening, a biologist and ex-communist, and has an intermittent affair with Jean Tatlock, a troubled communist psychiatrist whose death appears to be a suicide.

When nuclear fission is discovered in 1938, after the Germans succeed in splitting the atom, Oppenheimer realizes it can be weaponized. In 1942, during World War II, U.S. Army Colonel Leslie Groves, the director of the Manhattan Project, recruits Oppenheimer as the director of the Los Alamos Laboratory to develop an atomic bomb. Oppenheimer fears the German nuclear research program, led by Heisenberg, might yield a fission bomb for the Nazis sooner. Oppenheimer assembles a team consisting of Rabi, Hans Bethe, and Edward Teller, and collaborates with the scientists Enrico Fermi, Leo Szilard, and David L. Hill at the University of Chicago. Teller's calculations reveal an atomic detonation could destroy the world; after consulting with Albert Einstein and having Bethe do his own calculations on the matter, Oppenheimer concludes the chances are "near zero". Teller attempts to leave the project after his proposal to construct a hydrogen bomb is rejected, but Oppenheimer convinces him to stay.

After Germany's surrender in 1945, some scientists question the bomb's relevance. Oppenheimer believes it would end the ongoing Pacific War and save lives. The Trinity test is successful, and President Harry S. Truman orders the atomic bombings of Hiroshima and Nagasaki, resulting in Japan's surrender. Though publicly praised, Oppenheimer is guilt-ridden and haunted by the destruction and mass fatalities. After Oppenheimer expresses his remorse to Truman, the president accepts responsibility for ordering the bombings, but also berates him and dismisses his plea to cease further atomic development. As an advisor to the United States Atomic Energy Commission (AEC), Oppenheimer's stance generates controversy, while Teller's hydrogen bomb receives renewed interest amidst the burgeoning Cold War. AEC Chairman Lewis Strauss resents Oppenheimer for publicly dismissing Strauss's concerns about exporting radioactive isotopes and for recommending negotiations with the Soviet Union after the Soviets successfully detonate their own bomb. Strauss also believes that Oppenheimer denigrated him during a conversation Oppenheimer had with Einstein in 1947, though he had in fact expressed his belief that he had caused a chain reaction that would one day destroy the world.