Villains are the mainstay of any good adventure. With very few exceptions, there is always some form of evil mind plotting dark things in the background. Whether this is a mindless mob of creatures that just happens to be devouring the locals, or a masterfully devious court magician manipulating a king to sinister ends, you can't get away from the guys.
This blog post aims to assist you in building memorable villains that are more than just numbers on a sheet of paper. If you're a player and not a game master, the character building advice in here might help you too, but this is specifically geared towards the folks weaving the story behind the encounters.