Final answer:
The foil of a story is a character whose personality is the opposite of the protagonist, used to provide a contrast and emphasize the main character's traits.
Step-by-step explanation:
The foil of a story is a character whose personality is the opposite of the protagonist. A foil is used to highlight and accentuate the traits of the main character by providing a contrast. For example, in William Shakespeare's play Romeo and Juliet, Mercutio acts as a foil to Romeo, as he has a lively and humorous personality compared to Romeo's somber and romantic nature.
Learn more about Foil of a story