Richard Feynman was born on May 11, 1918, in Far Rockaway, Queens, New York; his parents were Jewish, although they did not practice Judaism as a religion. The young Feynman was heavily influenced by his father who encouraged him to ask questions to challenge orthodox thinking. His mother instilled in him a powerful sense of humor which he kept all his life.

As a child, he delighted in repairing radios and had a talent for engineering. He kept experimenting on and re-creating mathematical topics, such as the half-derivative (a mathematical operator, which when applied twice in succession, resulted in the derivative of a function), utilizing his own notation, before entering college.

Feynman received a bachelor's degree from the Massachusetts Institute of Technology in 1939, and was named Putnam Fellow that same year. He received a Ph.D. from Princeton in 1942. Feynman's thesis applied the principle of stationary action to problems of quantum mechanics, laying the groundwork for the "path integral" approach and Feynman diagrams. While researching his Ph.D., Feynman married, Arline Greenbaum.

At Princeton, the physicist Robert R. Wilson encouraged Feynman to participate in the Manhattan Project—the wartime U.S. Army project at Los Alamos developing the atomic bomb. He visited his wife, who had been diagnosed with tuberculosis, in a sanitarium in Albuquerque on weekends, right up until her death in July 1945.

He immersed himself in work on the project, and was present at the Trinity bomb test. Feynman claimed to be the only person to see the explosion without the dark glasses provided, looking through a truck windshield to screen out harmful ultraviolet frequencies.

As a junior physicist, his work on the project was relatively removed from the major action, consisting mostly of administering the computation group of human computers in the Theoretical division, and then, with Nicholas Metropolis, setting up the system for using IBM punch cards for computation.

Feynman's other work at Los Alamos included calculating neutron equations for the Los Alamos "Water Boiler," a small nuclear reactor at the desert lab, in order to measure how close a particular assembly of fissile material was to becoming critical. After this work, he was transferred to the Oak Ridge facility, where he aided engineers in calculating safety procedures for material storage (so that inadvertent criticality accidents could be avoided). He also did crucial theoretical and calculation work on the theoretical uranium-hydride bomb, which was later proven to be infeasible.

Los Alamos was isolated; in his own words, "There wasn't anything to do there." Bored, Feynman indulged his mischievous sense of humour to mock a self important director (one of the few non-scientists on site). The director's only important responsibility was for document security. He irritated Feynman and other scientists with petty rules for handling documents. Feynman embarrassed the director by breaking into the document safe and leaving a mischievous note. The Director responded by procuring a series of ever more sophisticated safes, each time thinking finally to have outsmarted Feynman, only to discover in short order a new note in each new safe.

As a drummer, Feynman would find an isolated section of the mesa to drum Indian-style. These antics did not go unnoticed, but no one knew that "Injun Joe" was actually Feynman. He became a friend of laboratory head J. Robert Oppenheimer, who unsuccessfully tried to court him away from his other commitments to work at the University of California, Berkeley after the war.

After the project, Feynman started working as a professor at Cornell University, where Hans Bethe (who proved that the Sun's source of energy was nuclear fusion) worked. Feynman felt uninspired there; despairing that he had burned out, he turned to less useful, but fun problems, such as analyzing the physics of a twirling, rotating dish, as it is being balanced by a juggler. (As it turned out, this work served him in future research.) He was therefore surprised to be offered professorships from competing universities, eventually choosing to work at the California Institute of Technology in Pasadena, California, despite being offered a position near Princeton, at the Institute for Advanced Study (which included, at that time, such distinguished faculty as Albert Einstein).

Feynman rejected the Institute on the grounds that there were no teaching duties. Feynman found his students to be a source of inspiration and also, during uncreative times, comfort. He felt that if he could not be creative, at least he could teach.

Feynman is sometimes called the "Great Explainer"; he took great care when explaining topics to his students, making it a point not to make a topic arcane, but accessible to others. His principle was that if a topic could not be explained in a freshman lecture, it was not fully understood yet. He opposed rote learning and other teaching methods that emphasized form over function, everywhere from a conference on education in Brazil to a state commission on school textbook selection. Clear thinking and clear presentation were fundamental prerequisites for his attention.

During one sabbatical year, he returned to Newton's Principia to study it anew; what he learned from Newton, he also passed along to his students, such as Newton's attempted explanation of diffraction.

Feynman did much of his best work while at Caltech, including research in: