I want to recommend Jagdish Mehra's biography of Richard Feynman. "The
Beat of a Different Drum, the Life and Science of Richard Feynman "
Mehra who is a physicist goes into great detail on Feynman's
scientific work including the genesis of his Sum over Histories formalism, the
result of quantizing the Wheeler Feynman Absorber theory. There is also of
course a lot of fascinating personal information about Feynman, an
extraordinary physicist, an extraordinary Human being.