Foil characters make the characteristics and personality of the protagonist stand out. A foil character may be an enemy or a friend. A character that reflects (like shiny foil) the attributes of another character is a foil character.The foil character’s characteristics and personality serve as a contrast to the main character. They are named after the medieval practice of placing a metal foil around a gemstone to make it shine brighter. Foils are a great way to develop the protagonist’s characterization without dropping an anvil of a message upside your reader’s head. Foils often have conflicting personalities and dissimilar physical features. Through the use of the foil a protagonist’s background, upbringing and current position in society can be examined. The foil can share similarities in the given areas or have completely different circumstances in life. In the classic good-guy versus bad guy scenario, both the hero and villain can be considered as foils of each other, in that each acts to show how the other behaves in certain situations.
However, as virtually any story with multiple characters can contrast the characters to show greater depths to them, regardless of what side they are on in the good versus evil equation. In fact, good versus evil doesn't have to come into the picture at all. Sometimes, also, a foil is a secondary, flat character that comes on stage, sparks a response, then fades from the story. More often, though, the foil is a recurring character that has a personality, or an opinion of things, that is different from another recurring character. Many intentional foils are depicted as physical contrasts to the main character. Thin vs. fat and tall vs. short are among the commonest way of setting up contrast. Similarly, when the hero's love interest is blonde, the villainess tends to have dark or red hair; when the villainess is blond, the hero's love interest tends to be dark or red haired.
As implied earlier, virtually any two characters or character-types can serve as foils to each other if they're put together properly and a little good writing goes into the creation of them. However, there is a surprisingly large number of character-types that exist primarily for the purpose of being a foil, usually to the main character - or in the case of a set of characters, to each other.
www.eng.fju.edu.tw/English_Literature/19th_c/wuthering_heights.htmCritical Perspectives on Chinua Achebe- C.L. Innes and Bernth Lindsfors.
The Writings of Chinua Achebe- Killam Douglas