villain: (noun) 1. a wicked or malevolent person; 2. (in a novel, play, film, etc) the main evil character and antagonist to the hero
The biggest problem I see in villain descriptions is that the writer obviously hates their villain. The villain is the bad guy/girl who throws obstacles (among other things) into the way of the hero/heroine and is an all around nasty piece of work. However, the villain becomes a very flat or ineffective when the writer dislikes the villain. Not spending enough time developing them often puts a hamper on the story, because the writer hasn’t taken the time to organize and utilize the character.
A good litmus test of how well a story is written circles back to how effective the protagonist is at resolving the major conflict. Conflict is often (but not always) created by the antagonist, ergo the more creative and challenging the antagonist is, the more creative and challenged the protagonist is.
For example, in a case of bad writing that appears far too often in romances, the villainess hates the heroine for having the hero’s attention. She appears randomly in the middle of the story, plots to harm the heroine in an insipid, color by numbers method, then her plan fails and she is quickly disposed of and the hero and heroine live happily ever after. Did you feel cheated by that story? Probably. Did the hero and heroine become better characters? Not really. It was easier to make the villainess the scapegoat or deus ex machina than having the characters think critically.
So what sets great villains like Iago and Lord Voldemort apart from these kinds of stock characters? They’re characters we love to hate because they’re so damn brilliant we can’t help liking them or being in awe of what they do. The writers of these characters took the time to flesh them out, to give them whole personalities and complex motivations.
Harry Potter’s development throughout all seven books is juxtaposed by Lord Voldemort’s own development. Each book contains a piece of Voldemort’s past and how he has gotten to the point where Harry must fight and defeat him. Voldemort is part of Harry, they’re linked by that night Harry lived. By the time Harry has to face him, the readers have a multi-dimensional view of this madman. The readers are not just invested in Harry’s success, but Voldemort’s failure. It makes Harry’s challenge greater, thus his story becomes more epic.
Guess what else? The writer is the villain. The writer is the person raining fire and brimstone on the protagonist. The writer is the person who shakes the character out of bed that Monday morning and kills his goldfish in the afternoon when ninjas attack. The failure of the villain to create conflict is the failure of the writer to create conflict.
So writers, before you start to wish bad things upon your villain, please take the time to get to know them, let the reader get to know them, then feel free to throw them off a cliff into the fiery hellhole.