A hero is a man or woman (then often called a heroine), traditionally the protagonist of a story, legend or saga, commonly possessed of powers far beyond that of a standard human, which enable him or her to perform some truly extraordinary, beneficial deed (a "heroic deed") for which he or she is famous. These powers are sometimes not only of the body but also of the mind.
A person cannot be a hero without first performing a heroic deed. Traditional deeds are slaying of monsters and saving people from certain death. A hero always fulfills the definitions of what is considered good and noble in the originating culture.
Sometimes an actual person might achieve enough status to become a hero in people's minds. This is usually complemented by a rapid growth of myths around the person in question, often attributing him or her with powers beyond those of ordinary mortals.
Well-known heros approach the gods in status in some cultures.
A book of recent fame, dealing with the telling of heroic stories, is called The Hero with a Thousand Faces.