What term refers to a character that shows qualities in contrast with another character to highlight traits?

The term "foil" refers to a character who possesses qualities that contrast with another character, typically the protagonist. The purpose of a foil is to highlight specific traits or attributes of the main character, allowing the audience to gain a deeper understanding of their personality, motivations, and development.

For example, in many literary works, a courageous hero may be contrasted with a fearful companion, which emphasizes the hero's bravery. This contrasting relationship helps illuminate the characteristics of both individuals and can advance the plot or theme of the story significantly.

The other terms do not serve this specific function. A doppelganger typically refers to a character that acts as a double or mirror image of another character, which does not emphasize contrasting traits. The protagonist is the main character of the story, while the antagonist opposes the protagonist, but these roles do not inherently focus on contrasting qualities for the purpose of highlighting traits in the way that a foil does.