Foil (literature)

 Don Quixote and his sidekick Sancho Panza, by Gustave Doré: their character contrasts are made manifest not only by their behavior, but their physical appearance.]] A foil is a character that contrasts with another character (usually the protagonist) in order to highlight various features of the main character's personality: to throw the character of the protagonist into sharper relief. A foil usually has some important characteristics in common with the other character, such as, frequently, superficial traits or personal history.

A foil's complementary role may be emphasized by physical contrasts. For example in Cervantes' Don Quixote, the dreamy and impractical Quixote is thin in contrast to his companion, the realistic and practical Sancho Panza, who is fat. Another popular fictional character, Sherlock Holmes is tall and lean; Doctor Watson, is often described as "middle-sized, strongly built." The "straight man" in a comedy duo is a comic foil. While the straight man portrays a reasonable and serious character, the other portrays a funny, dumb, or simply unorthodox one. The humor in these partnerships derives from the interactions between these drastically different personalities.

In some cases, a subplot can be used as a foil to the main plot. This is especially true in the case of metafiction and the "story within a story" motif. One example of a plot being used as a foil can be seen in the graphic novel Watchmen, where a comic book within the Watchmen universe presents a story similar to that of one of the main characters.

Origins
The term foil refers to the practice of putting dark, polished metal (a foil) underneath a gemstone to make it shine more brightly.

It is also likely that widespread use of the word "foil" in literature comes from the play Hamlet by Shakespeare, in which Hamlet says that "I'll be your foil, Laertes: in mine ignorance / Your skill shall, like a star i' the darkest night, Stick fiery off indeed" (Act 5 Scene 2)

Other examples of foil characters in Shakespeare's King Lear are: Oswald and Kent, Edmund and Albany, and Cornwall and Gloucester.