Two new species of braconid wasps (Hymenoptera: Braconidae: ... by Cauich-Kumul, Roger; Lopez-Martinez, Victor; Garcia-Ramirez, Maria De Jesus; Delfin-Gonzalez, Hugo; / Florida Entomologist.
The most well-known dramatic foil character in Romeo and Juliet is Mercutio. He acts as a direct opposite of the protagonist, Romeo. Mercutio is a skeptic, while Romeo is a romantic. Foils are used to bring emphasis to the qualities of another character, and they often serve as comic relief. Continue Reading.
In fiction, a foil is a character who contrasts with another character (usually the protagonist) in order to highlight particular qualities of the other character. 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. The word foil comes from the old practice of backing gems with foil in order to make them shine more brightly.