Major characters, such as your protagonist and antagonist, will each follow a default archetype during the story, with a protagonist following the hero archetype (usually) and the antagonist, the shadow archetype. However, please note that these two archetypes can also be present in other characters at certain points during the story.

A secondary or minor character may not be the hero of the story, but that person can exhibit heroic traits or become heroic during certain events in the story, and readers will love them for it.

On the other hand, even your protagonist's allies can exhibit some traits of the shadow archetype at different points, depending on that character’s personality and what the events bring forth in his or her actions. When we show our protagonist help a friend overcome darkness, we create powerful emotional connections between the reader and those characters. For instance, in Star Wars: A New Hope, Han Solo overcomes his mercenary tendencies to heroically save Luke Skywalker's life, just in time for Luke to destroy the Death Star space station.

THE HERO

Now, let's examine the Hero archetype.

The most common protagonist type is the hero, a person who sets aside his or her own desires or needs to help others.

Not every protagonist is a true hero, though those terms are often used interchangeably. Hero can refer to a male or female protagonist, though in some cases a female protagonist is still called a heroine, especially in romance novels. However, that distinction is not used as often as it once was.

The function of the hero archetype is to serve and sacrifice.

The one quality a protagonist must possess in order to fill the hero archetype is a willingness to sacrifice him- or herself for the good of others.

A character in the role of hero personifies the search for identity. For example, Luke Skywalker in Star Wars: A New Hope doesn't want to become a farmer as his uncle desires for him. He wants to be a pilot and go to the academy and, deep down, to do something about the terrible Empire that rules the galaxy.

The true heroic protagonist also shows a willingness to grow and change, takes action or reacts in a way that drives the events of the plot, is willing to take the big risks (even if he or she is afraid), has some kind of universal appeal, and has a willingness to give up something that's important to him or her in order to reach the new story goal and achieve the character's true need.

In a post on the three keys to writing a compelling protagonist, I discussed how the protagonist should have not only an initial story goal, but a true need. So, there should be something greater that the protagonist needs even more than the thing he or she wants most at the beginning.At some point in the story, the protagonist's aim shifts from that initial story goal to pursuing the true need that he or she discovers. This often requires some kind of sacrifice.

Keep in mind that the hero doesn't always have to be good. In fact, he or she shouldn't. This character should have flaws just like any other, and those flaws can run pretty deep in a protagonist.

When the hero is the protagonist, the reader experiences the events of the story through that person's eyes. So, they must be able to relate to this character more than any other. One key to this is making sure your protagonist's motivations and goals are clear, understandable, and relatable.

Readers will see themselves in this character's quirks, vices, and deepest fears, while wanting to imitate the hero's admirable qualities. For this reason, the hero's internal and external problems must not be trivial. They must be important and those that the hero can solve him- or herself, even if that seems impossible at first. To be a protagonist, your character needs to be the hero of his own story, or fail to do so if you're writing a tragic character arc. (For more on character arcs, check out this post.)

THE SHADOW

Now, let's discuss the Shadow archetype. Its function is to destroy.

Villains and the protagonist's other enemies serve in the role of shadow. They exist to create threat and conflict and give the protagonist something to struggle against.

The protagonist's arch enemy isn't the only character who can take on the role of the shadow. Villains often surround themselves with minions, thugs, goons, etc.

The shadow isn't picky about its loyalties, though. Anyone can take on the role of the shadow during the story. Even an ally can become antagonistic from time to time. From the school bully to the protagonist's BFF, shadows lurk around every corner, waiting to derail the protagonist's plans.

Shadows do not have to be a character at all. In Star Wars, the dark side of the Force is just as much a shadow for Luke Skywalker as Darth Vader, his arch enemy.

In essence, the shadow is a negative or corrupted reflection of your protagonist's qualities. It can represent his or her darkest desires, untapped resources, or greatest fears. The most terrifying villains and creepiest monsters are those that embody the things we dread most, especially things we fear to find within ourselves.

This archetype is most effective when it mirrors the protagonist and shows readers the twisted person the hero could become.

In stories that focus on internal conflict, the shadow is the part of the protagonist that he or she tries to hide.

While this concealed trait or desire is often a bad one, it can be a positive one, just contrary to the version of himself the protagonist wants to portray to the world. For instance, your protagonist could be a football star who secretly wants to write poetry, or a ballet dancer who wants to drive monster trucks. If your protagonist is a loner or a tragic figure, the shadow may be positive qualities he or she has suppressed.