1. Think of your antagonist as the potential outcome for your protagonist. We hear a lot about how antagonists should contrast with your protagonist, but few people recognize how many great antagonists are actually very much like the protagonist. General Zod is exactly what humanity fears Superman COULD become (an alien out to dominate and/or destroy humanity). Harry Potter fears constantly that he will become like Voldemort, because he can also speak with snakes (in fact, a part of Voldemort literally lives within Harry). Darth Vader is the Jedi knight who gave into the temptation of the dark side of The Force, something Luke must constantly struggle against. Khan in Star Trek loves his “crew” just as much as James Kirk loves his.
The struggle between protagonist and antagonist mirrors an internal struggle within the protagonist. Remember that internal conflict when composing the external battles.
2. Give your antagonist credibility within their society. Often, antagonists were at one time evolved heroes who are currently still riding a wave of good will because of some good thing(s) they did in the past. That gives them tremendous power, and makes it difficult for the protagonist to defeat them. Even dictators, i.e. President Snow in The Hunger Games, have their supporters who believe they are working for some greater good. Many of his supporters believed Hitler was the savior of Germany. Without a strong and credible support system, they will not be good opponents.
Even if you’re writing a contemporary story, say, set in a high school or the work place—remember the power of popularity, and how that can make life awesome for some and miserable for others.
3. That said, don’t make them SO powerful it’s impossible to believe they can be defeated. Just like your protagonist, your antagonist should be deeply flawed. Something needs to help bring them down in the end. Many are felled by things like arrogance, overreach, fear—even love. Make certain you give them some chinks in their armor.
4. Give your antagonist positive aspects to their character. The days of the mustache-twirling villain are long gone. Just like your protagonist, your antagonist should be a study in contradictions. Hannibal Lechter is an example of an antagonist who charms readers and audiences into liking him. Norman Bates can be a very polite and kind. Tywin Lannister can be utterly ruthless and a complete bastard to his children, but he can also speak to a servant on an equal level.
5. Give your antagonist motivation(s) that make sense—at least to him or her. Dorothy dropped her house on top of the Wicked Witch of the West’s sister. Even though it wasn’t intentional, the Munchkins see her as their heroine for doing it. It’s a pretty good reason for the Witch to hate her.
6. Not every antagonist has to be a villain. Which is why this article is not called tips for creating a great villain. Antagonists can be good people who simply happen to be working in opposition to the protagonist. You see this a lot in stories about anti-heroes. For instance, in Breaking Bad, Walter White’s brother-in-law Hank, a cop, is a good guy—Walter even likes him—but is also his natural antagonist.
It doesn’t have to be limited to anti-hero stories. I would argue that in romances, the hero and heroine are each other’s antagonists. Parents can serve as antagonists to their children (or vice versa) even if there is a loving relationship between them.
7. Not every antagonist has to be a person. The forces of antagonism can be a thing (a hurricane, a zombie invasion, an iceberg meeting up with a sinkable ship). Or, the antagonist can be the protagonist—in other words, the protagonist’s own worst enemy is herself.
8. The protagonist can face more than one source of antagonism. Though you should vary the level of antagonism from character to character. Harry Potter has to face several antagonists besides Voldemort, including Draco Malfoy, his classmate. In Malfoy’s case he’s basically just a typical school rival–which is eventually used by Voldemort, the story’s personification of evil.
9. Characters who seem to be the protagonist’s allies can turn out to be a source of antagonism, and vice versa. In Braveheart, Robert The Bruce seems to be an ally of William Wallace, and then betrays him. Snape seems to be Harry Potter’s antagonist, when in reality he has been protecting him from Voldemort. In The Hunger Games, Katniss is convinced that Peeta is her enemy, when he’s not.
Change it up sometimes. Readers love to have their expectations of characters challenged, and that’s just as true of antagonists as any other characters in your story.