In this continuation of our biography of the life and scientific work of Richard Feynman, we look at the work for which he would win his Nobel prize. Beginning with his move to Cornell after the end of the Manhattan Project, we cover his full development of the path integral formulation of quantum mechanics, it's application to renormalization of quantum electrodynamics and the development of his Feynman Diagram. We also consider the contributions of Julian Schwinger and Freeman Dyson.