Nemesis, Boss, Big Bad, Main Villain: if you’re running a table-top role-playing game campaign, you’re likely going to want to have a good main adversary for your players to eventually confront. Role-playing games thrive on conflict, after all; and what better way to personalize that conflict than to, well, personalize that conflict? If done properly, a good villain can make for a memorable campaign climax.
Relax. It’s not as hard as it might sound. You just have to think things through, a little ahead of time. The very first thing that you need to work out? Well… just because you want to have a main adversary, is that actually a good idea? After all, you may end up with a group of players that really isn’t all that interested in destroying the Lich-King of the Southron Wastes, or whatever main villain you came up with. If having a main villain is that important to you, then perhaps you should check with your players ahead of time and see whether they’re interested in that sort of game, or will at least go along with it in good enough humor. …Actually, talking to your players about the campaign is just a good idea in general.
Once you’ve established that you’re going to have a villain, now’s the time that you have to decide what kind of villain you want to play. Yes, you. The players are going to be living inside their characters’ heads; you’re going to be living inside your main villain’s. You don’t have to like him, her, or it as an entity — in fact, it’s probably best for your ethical well-being that you don’t — but you should be able to like playing the villain. This is going to be your best chance to get in some of the (hopefully) quality role-playing that your players take for granted; don’t waste it on a role which makes you uncomfortable, confused, or (worst of all) bored.
Then comes the KISS principle: “Keep It Simple, Stupid.” This is one of two traps that game-masters (GMs) can get into: creating an over-complicated villain. Not ‘complicated:’ ‘over-complicated.’ Players being players, they will likely wish to push for a confrontation with the main villain, preferably when they would have a real or perceived advantage during the encounter. What this means in practical terms is that you will probably have at least one situation in your campaign where you have to think and decide quickly what your main villain would do under unusual circumstances. If you have a good feel for your villain — because you have not over-complicated his or her personality and habits — then improvising on the spot will not be too difficult. If you do not really understand your own creation, well, the campaign might well implode at that point.
By the way: this does not mean that you cannot have a baroque super-villain with ornate schemes and meticulous planning. If you can do it properly, and if your players will not be driven mad by the experience. Just remember that role-playing games aren’t books or movies: you can’t always swiftly explain or visually show a character’s motivations or drives. Broad strokes are sometimes the only strokes that you will get.
Lastly, I’m going to say something that some people will find mildly controversial. Unless you are explicitly playing a campaign where both you and your players know ahead of time that the players’ characters are doomed (and people do play and enjoy those sorts of campaigns), the ultimate purpose of your villain is to lose. Sure, the villain can win if the players mess up something, or come up with the wrong plan, or simply don’t treat the campaign with even minimal respect; but your villain is supposed to go over the cliff in the end, snarling defiance or shrieking in fear as the rocks rise up to meet him.
Some GMs sometimes don’t want that to happen, and that’s understandable: people spend a good bit of creative juice creating campaigns, and you can invest yourself in your characters. But a good GM must in the end be ready to readily kill that which he loves. So should the PCs, of course, but there are more players than GMs at every table; and the GM has more opportunities to provide the necessary sacrifice.