The Hero with a Thousand Faces, 1949
Campbell explores the theory that mythological narratives frequently share a fundamental structure. He calls the motif of the archetypal narrative, “the hero’s adventure”. In a well-known passage from the introduction Campbell summarizes the monomyth:

A hero ventures forth from the world of common day into a region of supernatural wonder: fabulous forces are there encountered and a decisive victory is won: the hero comes back from this mysterious adventure with the power to bestow boons on his fellow man.