The range of characters available to the screenwriter is unlimited. But, as with anything to do with screenwriting, in practice it's pretty simple.
I'm not going to talk about background characters, here. If anything, I'm going to talk about character function.
Characters exist for a reason - and, if they don't, they shouldn't be there in the script. They must be doing things, fulfilling a purpose, adding to the brew. Always ask yourself: is this character important? Vital? Really adding to the script? Or have I simply found a character I like, but who may not belong in this story?
Certain character types are indispensable. They keep cropping up. There are four of them, and while it isn't necessary to have all four in a script, it's difficult to avoid having at least two of them.
These four more-or-less essential characters are:-
So - looking at them in turn ...
1. THE HERO. Try telling a story without this one.
Now, first of all, the HERO and the PROTAGONIST are not always one and the same. Usually, but not always.
The word PROTAGONIST comes from the Greek: it means 'first actor' or 'first contestant' (a memory of the time when drama was a competitive sport, as well as the struggle that lies at the heart of drama). The PROTAGONIST is simply the main player or lead character.
There are certain rules governing heroes, however. First, the word HERO. It again derives from the Greek and means, essentially, one who protects and serves. A PROTAGONIST does not need to engage in self-sacrifice; a HERO does.
In fact, the story of the HERO is universal. There is often something unusual or miraculous about their birth. They are often raised apart from their parents. They answer a certain 'call'. They make the journey into the World of Adventure for the good of their society. They struggle, they suffer, they bring back the magical key, the secret, the vital clue. They make their world a better place and, as a result of their endeavours, they GROW. They CHANGE. Their personality becomes stronger, fuller, more complete, as a direct result of the journey they've undertaken and the struggles they have undergone along the way.
2. SHADOW. Or, if you prefer, the VILLAIN, NEMESIS, RIVAL or BADDIE. But I prefer SHADOW. Thanks to Dr Carl Jung we know that every individual personality has a Shadow, which is composed of those elements of our psychological make-up that we don't like. We project them onto other people, or even other races.
When somebody takes an instant dislike to somebody else, that's usually the Shadow at work. For example, I don't want to think of myself as a conceited show-off, so when I meet someone who seems to be a conceited show-off I don't like that person. Why? Because, deep down, they remind me too much of my darker self.
As we know from 'Star Wars' (in fact, 'The Empire Strikes Back'), the SHADOW is not necessarily the polar opposite of the HERO. Psychologically, the SHADOW consists of those elements in the HERO's personality which have not been integrated. Thus, when we discover that Lord Vader is Luke's father (shock! horror! hold the front page!) what we're really learning is that the Dark Side has been present in Luke all along. He can resist it or he can assimilate it. Luke is a goodie (boringly so) because he opposes the evil forces. But the SHADOW is a function of the HERO's personality. Fighting it is not always the answer. Turning the negative aspects of the SHADOW into positive ones (making a friend of the SHADOW) creates psychological completeness.
But, of course, that seldom happens. In our shoot-'em-up world, the SHADOW must be destroyed. (What a better world it would be if our stories taught us to integrate the SHADOW side of ourselves, rather than projecting it onto others and then destroying them: the War On Terror is, in many ways, a war between the West and its Shadow, and wars like that can never be won).
So, the SHADOW is the HERO's 'opposite', the Yin to the HERO's Yang.
3. SIDEKICK. Sometimes called REFLECTION or ECHO. But SIDEKICK is better, because we all know what that means.
A SIDEKICK is usually the HERO's friend. They exist to make the HERO look better at what they do. Think of Sherlock Holmes and Dr Watson: Watson is a clever guy, but Holmes is miles ahead of him.
In many movies, the SIDEKICK doesn't make it to the end. This, again, is part of demonstrating how amazing the HERO is. The HERO survives, the SIDEKICK doesn't. Ergo, the HERO is better than the SIDEKICK.
The SIDEKICK can be thought of as a representative of the audience. They get us closer to the HERO, and show us how much better/braver/cleverer the HERO is than we are. Because of their friendship, the SIDEKICK can have conversations with the HERO that others can't. So the SIDEKICK sheds a new light on the HERO.
(The lighting image is quite a good one. The standard lighting set-up involves three light sources. Imagine the HERO as the subject. The HERO's confrontation with the SHADOW, the struggle between them, acts like the key light, thrusting our HERO into the spotlight and casting a large shadow. The SIDEKICK provides the backlight, lighting up the HERO from another angle. The LOVE INTEREST acts like the fill light, removing much of the shadow and giving us a somewhat softer, more rounded image of the HERO. Technical stuff, but a good mental image to hold in your head: the three satellite characters exist to 'light' the main character beautifully.)
4. LOVE INTEREST. Or ROMANCE. If the SHADOW is the enemy, the rival, and the SIDEKICK is a friend, the LOVE INTEREST is the lover, the prize, the object of desire. Attaining the love of the LOVE INTEREST is often the HERO's reward for having successfully undertaken the adventure.
So, we can picture our HERO in the centre of a space. The SHADOW stands before them in apparent confrontation (remembering, of course, that the SHADOW is composed of those elements of the HERO's psychology that the HERO doesn't like or want to know about). The SIDEKICK stands behind the HERO, making the HERO look braver, more romantic. The LOVE INTEREST stands to the side of the HERO, and slightly in front, showing us the HERO's softer side.
As I said, all four are not compulsory. Sherlock Holmes was seldom bothered by love interests. What is more - and here's the fun part - in the weird World of Adventure where the story happens, a character can switch from one function to another:
A SIDEKICK can become the LOVE INTEREST, or the SHADOW. The SHADOW might turn out to be the LOVE INTEREST (I think Jung would have loved that). In some stories, the main character is merely a Protagonist, and it is the LOVE INTEREST, or the SIDEKICK, or even the SHADOW, who turns out to be the HERO (undergoing tests and trials and emerging as a new, improved person).
So there's plenty of fun to be had with these four. You may not need them all in your story, but it's not a bad idea to have all four.
Remembering, of course, that the HERO, the SHADOW, the SIDEKICK and the LOVE INTEREST all have their own stories. Each of them has OBJECTIVES and OBSTACLES (yes, and INNER and OUTER ones).
Create four interesting major characters. Make sure they each have their own story (OBJECTIVE and OBSTACLE). Be prepared for them to change their function during the script. And ensure that the satellite characters exist to reveal the HERO, giving us three different angles on the HERO's character.
And then, you should have a pretty solid constellation of characters at the heart if your script.