Separating mythology from actual events in the life of Butch Cassidy has been made extremely difficult by the many stories told about him by family members, acquaintances, and writers after his presumed death in a Bolivian village. In an exhaustive search of reminiscences, newspapers, and books, Richard Patterson has written the definitive biography of the outlaw whose legend is rivaled only by that of Billy the Kid.

Born to a devout Mormon family in Utah, Robert Leroy Parker demonstrated early on the acquisitiveness and restlessness that would lead him into a criminal life. As a teenager,...