Character Foils

    WARNING: The following post contains at least one spoiler about the play Hamlet written by William Shakespeare
    Character foils. You might've heard about them in English class. Though in case you haven't, or if you have heard of it but haven't considered why they're important . . .
    A character foil is basically a character whose behavior and/or actions starkly contrast with another character's, and they're significant for not only classic literature but also current fiction for multiple reasons.
    Firstly, they help illustrate a folly. Using the classic example of William Shakespeare's Hamlet, the play's namesake and a character named Laertes foil each other. Their opposite behaviors and attitudes are shown as they react to the same event (their father's death) in very different ways. Hamlet takes a lot of time to think about what to do, hesitating, talking to himself, and experimenting. Whereas Laertes doesn't wait, hesitate, or really think at all; he immediately plows into plots to avenge his family. Both forms of action (over-thinking/procrastination and furious impulsiveness) are negative, and it's like William Shakespeare was showing the polar opposites of a spectrum and why they both should be avoided. Two themes in one without a moment of lecturing.
    Foils are also useful for creating conflict. People running in opposite directions on the same track lane are bound to smack into each other. Using the Hamlet example again, the prince of Denmark's mode of action is shown for many scenes before Laertes starts playing a revenge-seeking role. And when Laertes does start acting, it opens up a whole new door of opportunity for the play's villain, and creating serious problems (and ultimately a tragic end) for Hamlet.
    Characters who foil each other don't have to be enemies or rivals though. Elizabeth Bennet and her sister Jane Bennet from Jane Austen's Pride and Prejudice foil each other, and they get along fantastically. As do Sherlock Holmes and Dr. John Watson from Sir Arthur Conan Doyle's various Sherlock Holmes stories--they're complete opposites behavior-wise, but their differences often make them a stronger team. The fact that they foil each other also makes their friendship unique and memorable to this day.
    Other examples of character foils (at least in my opinion)  are America and Celeste from Kiera Cass's Selection series, Steve Rogers and Tony Stark from the Avengers movies, Peeta Mellark and Gale Hawthorne from Suzanne Collins's Hunger Games series, and Alby and Newt from James Dashner's Maze Runner series.
    Can you think of other character foils? Does your novel/short story in progress have one?