A character whose actions or qualities serve to heighten those of the hero through contrast is

A character whose actions or qualities serve to heighten those of the hero through contrast is called a "foil". A foil is a character who is used to emphasize or contrast the qualities of another character, usually the protagonist. The foil character may share certain traits with the hero but typically has opposite personality or behavior. This contrast highlights the hero's positive traits and makes them stand out more clearly to the audience or reader.