There are different terms that we use to categorize characters based on the function that they play in a work of literature. Many of these terms will likely be review for you.

The protagonist is the main character of a story, and it is the protagonist’s desire for justice, power, love, money, acceptance, and so on that drives the story’s plot. While oftentimes we think of the main character as the “hero” or “heroine” of a story, there are numerous examples from literature and film of protagonists who are not particularly good people. One such character is Shakespeare’s Macbeth; he is a power-hungry murderer, but still the protagonist.

The antagonist is the character who opposes the protagonist’s actions. Sometimes the antagonist’s relationship to the protagonist is an obvious one—Voldemort to Harry Potter, for instance. More often than not, however, the antagonist has different goals and desires than the protagonist, and is not simply the “bad guy.” In the play Antigone, for example, Antigone wants to bury her dead brother, who led a rebellion, but her uncle, King Creon (the antagonist), refuses to allow her to do so because the burial could cause further instability in the kingdom.

Minor or supporting characters are those whose actions or personalities complement or contrast with those of the protagonist or antagonist. They might not be essential to the plot of the story, but they round out the world of the main characters. As author Stephen King says in his novel, Revival:

In one way, at least, our lives really are like movies. The main cast consists of your family and friends. The supporting cast is made up of neighbors, co-workers, teachers, and daily acquaintances. There are also bit players: the supermarket checkout girl with the pretty smile, the friendly bartender at the local watering hole, the guys you work out with at the gym three days a week. And there are thousands of extras — those people who flow through every life like water through a sieve, seen once and never again. The teenager browsing graphic novels at Barnes & Noble, the one you had to slip past (murmuring “Excuse me”) in order to get to the magazines. The woman in the next lane at a stoplight, taking a moment to freshen her lipstick. The mother wiping ice cream off her toddler’s face in a roadside restaurant where you stopped for a quick bite. The vendor who sold you a bag of peanuts at a baseball game.

All of these minor characters build the world of the story, and bring it to life.

One of the primary differences between main characters and minor characters is the amount of effort the author spends in developing them. Main characters tend to be round characters, meaning they have a certain amount of complexity and several traits that define them; they also tend to be dynamic, meaning that they change in some way over the course of the text. Minor characters often are flat characters defined by a single characteristic, such as the mean teacher or the dumb jock, and they are often static, meaning they remain essentially the same throughout the story. There are exceptions to every rule, of course. It might be tempting to think of flat or static characters as being products of bad or lazy writing, but most authors rely on a variety of character types to create their literary works.

A foil is a specific type of character that contrasts with the protagonist, and thus highlights one of his or her significant character traits. One well-known example of a foil is Dr. Watson from the Sherlock Holmes books, movies, and television shows. Holmes is absurdly intelligent and intuitive, able to make rapid deductions that Watson is unable to process as quickly. Watson often has to ask questions and have Holmes summarize and restate things. Dr. Watson’s role is to make it clear that Holmes is so smart that even a doctor has a hard time keeping up with him.