Every story has a protagonist or protagonists. They’re the heroes, the viewpoint characters, the ones we root for—in roleplaying games, these are always the player characters. (It’s possible to have protagonists who are not player characters, but if your player characters are not protagonists there’s a good chance something’s going wrong.) A story also requires, to be interesting, that the protagonists have some sort of opposition or struggle—often in the form of antagonists. Antagonists are the villains, the “bad guys”, or at the very least, the characters who get between the protagonists and their goals. These descriptions can be much more complicated, but for the purposes of the discussion, the definitions above will suffice.
While a lot of the opposition player characters face in a D&D game is short term—monsters who last one single fight, or to the end of a given adventure—sometimes a DM will bring out long-term rivals or create a nemesis, a recurring character who time after time foils or escapes the player characters. This is not a bad thing, nor is it unique to roleplaying games. Comic books and serial stories in just about any medium have had these types of characters since well before D&D. Sherlock Holmes faced off against Professor Moriarty many a time, and the Joker from Batman is at least as iconic as Batman himself. In a roleplaying game, you can use a recurring villain or rival to create a sense of continuity as well as to give the players someone they love to hate.
There’s a complication, though. In fiction, we love to hate the recurring villain on behalf of the characters we’re reading about, but in a roleplaying game, a character who constantly foils the heroes and seemingly escapes their every effort to stop him can quickly become frustrating to the players. Constant escapes or a villain who always gets the better of the player characters regardless of their actions can make the players feel as though they are being shut down, or as though they are ineffective. Always be careful to give the players a chance to defeat the villains, and try not to cross the line between running a character they love to hate and running a character they just plain hate.
Don’t leave the characters in a position where they feel unsatisfied with their inability to overcome a recurring rival or nemesis. This doesn’t mean you need to let them kill off your favourite villains prematurely, but consider that there are other forms of defeat. Remember also that in D&D, death is not necessarily the end—a vile and murderous assassin might be slain by the players only to return a few adventures later as an undead creature. The trick to bringing a character who the PCs kill back is to give it time. Don’t have them immediately return as if nothing is wrong. Even in a case where the recurring nemesis successfully escapes the wrath of the players, take an adventure or three where they don’t show up at all before you bring them back around for another go. Using a recurring villain every adventure can feel like you’re rubbing in the players inability to stop them.
When you do give your characters a chance to finish off one of your recurring villains, though, make it grand, and make it memorable. Let the player characters relish and delight in their foes getting their long-awaited comeuppance. Don’t cheapen it by taking away their chance to avenge themselves for the slights they’ve suffered at the hands of the rival. Not every recurring character needs to be killed to be dealt with, either—some rivals who are not directly opposed or evil, but just keep getting in the way or one-upping the heroes could find themselves humiliated or imprisoned, forced to eat humble pie at the hands of the main characters.
Giving the characters someone to love to hate is great, but in the end, the satisfaction of victory over those special villains is what makes them work. A villain who can’t be defeated is one who provides nothing but frustration, and frustration is a good way to kill the enjoyment of a campaign forever. Don’t just hand over the victory, but don’t deny it forever, either. That’s the trick to handling recurring villains.