Fight Club

(1999)

Foil

Character whose main purpose is to offer a contrast to another character, usually the protagonist. The foil will have some things in common with the protagonist, but will be different in one or a few important ways. Foils highlight the key qualities of the main character and are convenient ways to complicate and deepen the characterization of the protagonist.

Basically, a foil is any character who makes traits of another stand out in sharp contrast.