Roots of evil are human passions

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.