I do it all because I'm evil,role playing games, although there's an important difference: villains from fiction tend to be more memorable, more believable. Rarely do we, as players of the game, lament the death of a great villain. Why is this so?
and I do it all for free,
your tears are all the pay I'll ever need.
— Voltaire, "When You're Evil"
In my experience, the villains encountered in our games are often killed off too quickly or their motives are less-than believable. How many Mad Wizards bent on destroying the kingdom have we seen? How many rapacious Bandits have we captured? If you look at the archetype villains through the history of D&D - very few are memorable and quite a few are just downright forgettable.
There are several important things you can do to make the villains more memorable in your game:
- What kind of villain are they? Are they a Card-Carrying Evil villain (like the Mad Wizard above)? Or something else, such as Knight Templar or a somewhat more subtle Well Intentioned Extremist? Is the villain also the Big Bad of the story/campaign? Figure out what kind of villain they are ahead of time and decide on some guidelines about how they should be role played both in and out of combat (and 'off stage', behind the scenes).
- What is their motivation? The card-carrying types don't need a motivation - they just do evil for Evil's sake. Other villains, however, should have some legitimate goals. At a very minimum a villain should have an elevator pitches worth of description that outlines their motivation. When mooks or minions are captured and questioned - bits of their boss's motivation might be revealed. Clues left behind in dungeons, urban settings, or other adventuring areas also give some clues. Believable motivations lend credibility to the villain, and the PCs can act on their expectation of those motivations.
- Give them Managers. And their Managers Minions. Unless the villain is a solo "bad guy", they should have at least one layer of mid-level managers. Those mid-level managers in turn should have a whole collection of minions and mooks. These are the guys that do all the villains boring grunt work. You know... things like burning villages, plundering tombs, capturing slaves, etc. Establish the motivation of the mooks and their managers too. Are they serving out of loyalty? Are they being paid? The managers (tribal chiefs, elites, etc) might have one set of motivations and the minions another. Regardless, setting up and defining these motivations can help shape the PCs perception of who this super villain is, and what they are up to.
- Don't Kill Them. Not Yet. Memorable villains show up more than once throughout the campaign either in spirit ("Dr. Madevil was just here!") or in the flesh ("Dr. Madevil, you won't escape us this time!"). Change up the ways in which the PCs face the villain or encounter their minions. Avoid making it expected that the villain is going to escape. You can also really keep the players on their toes by having several layers of villains; minor villains don't escape (cRPG equivalents of 'mini-bosses'). It's a bit of balancing act - one method I employ is to have the villains show up when the players are lowbies (somehow they escape or survive), again when they are mid level, and then have a big face off battle once they are 9th or 10th level. Spread it out over a few levels and the effect is amazing. That last battle, when the PCs finally defeat or capture the villain, is a gaming moment sometimes on par with the best that fantasy literature has to offer. I also like to use the Boss in Mook's Clothing Trope.
What to read more? For more villains and how to play them - head over to At-Will's post "The Vicious Virtues of Villany".