These are the bad guys.
Bad guys are often overlooked as simple plot devices, which is sad because a well-developed villain is a thing of dark beauty. Just like the Protagonists, they risk a lot- discovery, defeat, death, shame, and in a magical world sometimes worse- to pursue their agendas of doom.
When you make your villain, don’t be afraid to make him/her/it a real prick; he’s a hideously rotten turd, capable of anything to achieve his ends. This include sacrificing the innocent, making that which was pure cheap, and challenging entire nations to satisfy their ambition for power. On the other hand, don’t make them unnecessarily nasty. Save the bit about eating children unless it’s really relevant to the plot.
How developed should your villain be? Well, it’s a matter of artistry here. With a sufficiently developed background, the villain can become many things to the story you’re telling, even the main character!
Come again?A compelling villain has some hook, some kind of specialness that evokes strong emotions from the audience. Whether that emotion is positive, negative or waffles in between is up to you, but don’t be afraid to make your villains evil.
Your bad guy probably isn’t stupid, either.
If he was, he wouldn’t be in power. He uses minions to weaken the characters before the final showdown, he only fights on his terms (and fights dirty, at that).
A good villain is intelligent enough to cause entire nations trouble. He uses hostages, threats of destruction, lies, bribes and outright thuggery and murder. Sure, we knew that… but our jobs as writers are to make him seem as though he thinks there’s nothing wrong with what he’s doing, and make him seem to take joy from it while not acting like a maniac.
A good villain isn’t, as a rule, over the top.
Sometimes, however, the bad guy isn’t a person at all, but an unfeeling force of the cosmos or a looming disaster. In theses cases, the enemy is the ticking clock, the sense of impending doom that the PC’s have while betting on steadily dwindling chances of success. These “bad guys” are revealed in the way they change the lives of the common, decent folk of the world they threaten- such villains depend on others for their voice, and so we come back to our average NPC.