A character foil is a secondary character whose qualities contrast with another character, typically the protagonist, to highlight that other character’s traits more clearly. The foil’s opposite traits or behaviors make the main character’s strengths, weaknesses, motivations, or growth stand out. Key points about foils:

• Purpose: To illuminate the protagonist by providing a stark comparison.
• Common contrasts: bravery vs. timidity, selfishness vs. selflessness, impulsiveness vs. restraint, cynicism vs. idealism.
• Function in narrative: Helps readers understand the main character more deeply and can also advance themes or plot through showcased differences.

If you’d like, provide a specific work or characters, and I can identify who serves as the foil and explain how the contrast clarifies the protagonist’s portrayal.