The Greek term “a hero” refers not to someone with super powers, but to the protagonist (main character in an “agon,” a conflict or battle). As defined by Aristotle, it is one element of a “tragedy,” a drama in which a hero (a great man) falls from a great height due to a tragic flaw; there are other elements of the definition of tragedy involved, too, such as a “catharsis.”
The term “hero” has been transformed in modern times to mean someone who performs a brave or self-sacrificing act in order to “save” someone else, usually physically, but also in a metaphorical sense, "My teacher is my hero." Comic books have taken the term even farther, referring to fictitious figures with super-human powers, which they use for the general benefit of humanity, as “heroes.” The term may be used to refer, for example, to someone who saves a trapped person in a car crash, or a fireman who risks his own life to save a child in a burning building. Of course, the term has become a common exaggeration in everyday speech.