The most basic element of any story is the conflict. And this conflict generally arises between the protagonist and the antagonist. Two characters (at least, they're usually two separate characters) whose goals are at odds and who tend to butt heads. The antagonist tends to be harder to create than the protagonist, and if you do it wrong, you'll lose readers faster than my son loses his Legos.
What is an Antagonist?
Before you can create a good antagonist, you have to understand what exactly an antagonist is. On a basic level, the antagonist is the bad guy. This is the person who gets in the way of the protagonist (the good guy). The antagonist is the reason (or one of them) the protagonist doesn't get what he or she wants. Sometimes the bad guy is a direct threat to the good guy, but sometimes not.
Your antagonist can take many different forms. Usually the antagonist is a separate and distinct character intent on doing the protagonist harm. Other times, he or she will simply get in the way, foiling the plans of the good guy (either intentionally or by accident). Occasionally, the antagonist is not its own character, but a part of the psyche of the protagonist. This is rare and not all that easy to do, so unless you've been practicing, don't do this.
Creating a Believable Antagonist
One of my biggest problems with most novel is the haphazard way in which the bad guy is treated. The good guy (and all his buddies) get to be fully-formed characters, but the bad guy exists as a two-dimensional chunk of mud. If you want me (or anyone) to read your work, you need to put just as much effort into creating your antagonist as you do any other character.
Start by understanding exactly what the role of the bad guy is. Most bad guys don't have to carry the weight of the story (unless your antagonist is also your main character). The protagonist lurks in the background, waiting to get in the way. This doesn't mean he (or she, but I'm going to stick with he) doesn't have to be as real as anyone else in your story, but it does make your job easier if you don't have to worry about him on every single page.
The key to creating a realistic antagonist is to give him a story. Why is he the way he is? In my first novel, Arianna's Tale, the bad guy (who happened to be a girl) was the way she was because she was horribly jealous of her brother. This jealously drove her to destroy everything he had. She wasn't born evil, but her father was so focused on her brother, and her brother was so focused on anything but her, that she slowly slid down a very slippery slope. And ended up dead because of it (but that was at the end of the novel, of course).
In my second novel, the bad guy had originally been a good guy. But he was hopelessly corrupted by an even worse guy. That antagonist also died. Antagonist three was a man whose biggest failing was his attitude toward women. His father had raised him to believe they were nothing, not worth the ground they walked on. This attitude eventually led to his abusing the wrong woman. Women, actually.
And in my fourth (and current) novel? The antagonist is a woman, an enchantress. Except that she'd not exactly real. Instead, she's a construct, a creation whose sole purpose is to carry out the bidding of her master (who we won't meet until book five). But she's innately curious, and this actually helps the protagonist get out of a rather nasty situation.
The point is this: your bad guy (or girl, as the case may be) must have a story. There must be a reason for your antagonist to act the way he does. Most antagonists weren't born bad. Most of mine certainly aren't. Maybe the exception is the construct, but only because she was created by a bad guy. So when you're creating an antagonist, make sure they have a history and make sure you at least allude to that history. A good antagonist (ignore the oxymoron) will be more than just a bad guy. He will have a unique history that has made him who he is.
You might think there are no rules in creative writing, especially when it comes to writing a novel, but you'd be wrong. Of course there are rules, but these rules are more like conventions that help the reader understand and connect to your work. You can break these conventions, but doing so requires a firm understanding of them.
Beware of Stereotypes
We all know the stereotypes of both literature and film. The damsel who never contributes anything but needs constant saving. The evil dude wearing black. The ditsy blond. The idiot sidekick who is absolutely hilarious in his stupidity. These and many others are the stereotypes of storytelling.
Stereotypes have their place, but it's not in most literature. The exception is humor. If you're writing comedy, you might want to make use of exaggerated stereotypes. It can be funny to read about the ditsy blond or the sidekick who can't get anything right. If your hope is to induce laughter, literary stereotypes might be the way to do it.
If you're writing anything other than comedy, avoid stereotypes at all costs. There are a few instances where you might be able to make use of the black hat stereotype, but most of the others are out. Stereotypes are like cliches. Used right and sparingly, they can enhance your story. Overuse them and you're certain to turn off even the most determined of readers.
If you want to use a stereotype, try changing things up a bit. Perhaps your good guy wears black and walks around with a scowl on his face. Or maybe you have a guy who needs to be rescued by the beautiful damsel. By playing with the stereotypes you'll create greater depth in your characters and enhance your story.
Bring Out the Flaws in Your Characters
Everyone has flaws. You, me, the mailman, all of us. So one of the rules of creating fictional characters is that no one can be perfect. The exact flaws are many and varied, but every characters must have at least one flaw. Maybe the character in question has a fiery temper, maybe he never looks before he leaps, or maybe he's afraid of commitment. Whatever. But he needs flaws.
Once you have these flaws worked out, show them to the reader. Let your readers see these flaws, and consider exaggerating them when necessary. Not to the point of silliness (unless you're writing comedy), but enough that your readers don't for a minute think the character is perfect. Avoid the stereotypical traits (redhead with fiery tempers as their only flaw are really quite annoying), but flaws are what will make your characters come to life.
It's All in the Name
Naming your characters is an important thing, but there aren't a lot of rules regarding the names you choose. You can name your characters anything you'd like, but there are some conventions you might want to stay away from. Don't use anything obvious, such as naming the guy who's going to betray everyone Judas. Don't use the name Jezebel for a woman who is a false prophet or for someone who will eventually become a prostitute. Too obvious.
Play with names until you find something that fits. And don't let anyone tell you that you shouldn't use a name because it might offend someone. If you do that, you'll never be able to name any of your characters. Someone somewhere in the world will have that name, and that someone may possibly be offended. Choose a name based on your character, and don't worry about what people might think.
If you're worried that a close friend or family member may be offended by the use of their name, change the spelling. Vicki can become Vicky, David can become Daivid, Jamison can become Jamyson. This works especially well for speculative fiction (such as fantasy or science fiction), but odd names work in just about any genre.
Think carefully about your fictional characters and consider everything from names to personality traits. Your job as an author is to bring your characters to life. To do this, follow the most basic of rules and fill your characters with believability.
