One of the things that I’ve noticed throughout my experiences as a tabletop gamer and game master is that there are often times when villains are really the driving, dominant characters of the players’ adventures. They’re one of the few characters that the GM has almost unfettered power over, and when they’re done right they can become great backbones of an interesting campaign; when they go wrong, on the other hand, they become in-jokes and disparaging references.
The first thing to remember is that a villain is a narrative device. You have them to add interesting elements to your story, so don’t make them nothing more than a pile of numbers and a stereotype. On the other hand, it’s important to carefully design your villain; in most cases it’s pretty simple to keep characters alive in games, so you don’t need to make them as powerful as you’d think, so long as you make sure they avoid combat. Realistic villains work better than villains that don’t fit mechanically into the universe you’re playing in; save them through the narrative, even if that means they don’t always pose a great threat, and you’ll be making a more interesting character. Winning battles isn’t the only thing that makes a villain scary, and you don’t have to create a Final Fantasy-esque fifteen stage boss to make sure you annihilate the players for them to feel the villain’s impact.
It’s important that villains have a motive. If there has to be only one character in your campaign who is motivated in a way that adds to the story, it should be the main villain. It’s also important that villains’ motives be coherent and comprehensible. Saying that a villain hates everything good because is lame. A chaotic and evil character who commits heinous deeds for the thrill of it is a little better, but still not terribly satisfying. Villains should be just as much a part of the setting as anyone else, and need to have a role they fill; a corporate drone will have his own reasons to hinder the players.
However, villains also need to have power. It’s entirely conceivable that villains don’t have to have the same sort of power as the players, but they should be able to influence the plot. A world-renowned thief who always escapes with the goodies one moment before the players arrive (and frames them for it) can be just as good a catalyst to the campaign as any white-haired longcoat wearing pretty boy who just so happens to be able to summon astronomical bodies as weapons. Political figures make good potential villains, but it’s important to consider that they will often be very distant from the players, and there’s typically not much keeping the players’ characters from tearing them to bits person-to-person (barring, of course, the Level 20 Paladin King, but not every figurehead is combat capable), often very quickly.
Power is a very dangerous thing for a villain to have. It’s important to make villains powerful, and not just relative to the setting. If the players are ridiculously powerful, the villain should be too. If they are very weak, their villain might actually be a relatively minor power. In fact, it’s entirely conceivable that a villain may not grow at the same rate as the players; while this means they won’t be effective as a recurring adversary it gives the players an opportunity to see their growth in context. However, it’s important to also consider all the different powers that a villain has; the king won’t just step off his throne and smash the players into dusty smears, but will likely have bodyguards and even armies to send at them.
Another thing to consider with a villain is that they usually have the same obligations and concerns as a good player character does; a villain does not exist in a vacuum-it’s a common fallback to have angsty vengeful orphans become corrupted by their frustration and despair, but it’s also deleterious to creating an interesting character. Villains who are going to be tragic are practically required to have some ties; being the head of a corporation, trying to be an upstanding family man, or working for a mercenary company can all provide villains with an additional touch of humanity, and provide a way for the players to escape what would otherwise be a close call. Plus, it gives the players a chance to sink to the villain’s level or try to redeem them.
Finally, however, my central philosophy when I run a villain is to make sure that I can see the game world as they do. If I can’t buy that the repressive regime keeps people safer than being freely able to annihilate themselves by accident, my villain won’t look realistic. If your villain doesn’t hold a realistic worldview, your players may not buy into the game, which is one of the greatest harms a villain can cause.