This definitive book deals with the life and scientific work of arguably the greatest American-born theoretical physicist of the twentieth century. He was a great teacher, a born showman, bongo drummer, buffoon, and 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 on his path-integral formulation of quantum mechanics and quantum electrodynamics. Subsequently he developed the diagrammatic technique as a result of which the Feynman diagrams became ubiquitous in quantum field theory, elementary particle physics, and 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, and the limits of computation. Feynman had a unified view of physics and nature: he took the whole of nature as the arena of his science and imagination. Jagdish Mehra personally knew Feynman for thirty years. This book is intended for physicists at all levels; historians and philosophers of science; the scientifically literate general reader; biography enthusiasts.