The hero is defined by the villain
The NBC show Heroes has a lot of problems. It never quite lives up to its potential for a number of reasons. There is one thing I love about the show though. I love Sylar. Sylar is the bad guy. Occasionally you get the feeling that he would like to be a good guy, but deep down he is bad. His essential flaw is that he craves power. Specifically, he craves the superpowers of the other characters and he has a longing to take them, by force, generally leaving the other characters dead or at least deeply changed. Despite that, there is a certain glee to Sylar. He enjoys what he does, and he can readily explain why he does what he does. He’s also funny, and that always helps. I know many people absolutely hate Sylar. That’s fine too. Whatever the case, people care about the guy. People pay attention when he is on the screen.
The antagonist doesn’t have to be evil
Not all bad guys are quite as evil as Sylar. In some cases, they aren’t evil at all, they just have goals or intentions that run counter to the Hero. Watch a romantic comedy, and you will often see a good guy antagonist. For example, in Meet the Parents, Kevin is the ex-boyfriend of Greg Focker’s fiance Pam. Kevin is as close to the perfect guy as you can imagine. He is kind and creative. He is handy with a hammer and he is never anything but nice. He is so perfect, in fact, that Stiller’s character feels immensely threatened by the guy and worries that he is going to lose his fiance to him.
Antagonists represent obstacles
Antagonists come in many forms. They may be as evil and ruthless as Darth Vader or they may be as commonplace as an overbearing boss, a flirtatious ex-girlfriend, or an annoying little sister. The main role of the antagonist is to provide obstacles for the protagonist. The antagonist’s needs and desires in some way interfere with the needs and desires of the protagonist. The boss makes the protagonist work late when he should be with his wife. The flirtatious ex-girlfriend makes the protagonist doubt his commitment to the wife. The annoying little sister asks exactly the wrong questions just when they can cause the most trouble.
Every character has a story
When you are writing your novel, keep in mind that the antagonists have their own goals, their own needs, and their own hopes and desires. You may not agree with their worldview, but you should respect that it is important to them. The antagonists are, in their own minds, the protagonist of their own stories. Respect and understand their needs, and you will create antagonists that people want to read about.