Evil is the habit of taking pleasure in harming others.
Evil can be ignorant. That is, to have such high status that the character ignores everyone around him.
Evil likes to be seen as clever. There will always be conflict between characters when they are vying to be the most clever in the class. For one to be seen to be clever, someone else must lose out.
Evil opposes good. It tyrannises, restricts, represses, puts down, defies, and limits other characters. Whether the evil man employs obvious evil, such as murder and other forms of violence, or some of the more subtle forms of abuse, he has the same function in the story: to work against good.
Alfred Hitchcock said that the more powerful your antagonist, the more complex and dangerous the situation, the harder your protagonist must work to overcome it.
As you ratchet up the villain’s power, the energy rises. In almost every case a well-defined antagonist gives power to the story.
Well-intentioned antagonists are more interesting than black villains. On the simplest level, stories that contain villains are usually stories about good and evil. Usually the protagonist stands for the good, and the villain opposes the good.
Most villains are action-oriented. They steal, kill, betray, wound, and work against the good. Many of them begin to look alike. Often there’s a tendency for them to be poorly motivated, and one-dimensional. The reasons for their evil actions are rarely explained, as if people do evil just because they feel like doing it.
It is possible, though, to create dimensional villains. Depending on the style of the story, and how much depth you want to bring into it, villains can be just as unforgettable as any other character.
Smooth off some of the villain’s edges by showing some good points. Maybe he has to get to his daughter’s school performance. You can usually find complex psychology reasons for emotions such as fear, frustration, anger, rage and envy. So, let’s be fair: just as you would with the protagonist, tell us what motivates the antagonist.
Keep the main antagonistic off centre stage. His physical presence should be rare and reserved for climatic scenes of confrontation. In Bram Stoker’s Dracula, the Count seems more fearsome by his absence.
Remember: the more we know a character, the less they frighten us.