In addition to being the shiny silver stuff you use in cooking, or the verb meaning to thwart, there is a literary term called a foil. It refers to a secondary character that contrasts with one of the main characters in order to highlight certain qualities of that person.
Often a foil is the opposite in personality or attitude, but there can also be a contrast in appearance. If one character is self-confident and attractive, the foil may be timid and plain. A person who is logical and pragmatic may have a partner who is impulsive and daring.
Foils tend to emphasize the main characters’ good qualities, and can help give readers a better understanding of them as they interact with those who are their opposites.
Sidekicks, a term referring to close friends who accompany the main character on adventures or activities, are an example of foils. Famous ones I can think of off-hand are Batman and Robin, or Lone Ranger and Tonto. For 3 Stooges fans, Larry and Curly might be considered foils for Moe; or is Moe a foil for Curly? (I love Curly!)
What are some other famous foils or sidekicks? Do you use foils in your stories?