This definitive book deals with the life & scientific work of arguably the greatest American-born theoretical physicist of the 20th century. He was a great teacher, a born showman, bongo drummer, buffoon & iconoclast; a scientific magician capable of transcendental leaps of the imagination. During his career he was drawn into research on the atomic bomb before working out his path-integral formulation of quantum mechanics & quantum electro-dynamics. Subsequently he developed the diagrammatic technique, as a result of which Feynman diagrams became ubiquitous in quantum field theory, elementary particle physics & statistical mechanics. From 1950 he was based at the California Institute of Technology, where he worked on the superfluidity of liquid helium, the theory of polarons, the theory of weak interactions, the quantum theory of gravitation, partons, quark jets & the limits of computation. He'd a unified view of physics & nature. He took the whole of nature as the arena of his science & imagination. Jagdish Mehra personally knew Feynman for 30 years. In 1980 Feynman suggested he might do what he had already done for Heisenberg, Pauli & Dirac, that is write a definitive account of his life, science & personality. Mehra instantly agreed & subsequently spent several weeks talking to him. After Feynman's death Mehra interviewed almost 80 people who'd known him & aspects of his work. This book draws on this unique material & on Feynman's remarkable writings. It covers his childhood, his three marriages, his extraordinary range of interests. But most important, it deals with his scientific work in far greater detail than in any other biographical work. What has emerged is an authoritative account of Feynman's life & achievements.