Since the title character in Dexter is a literal serial killer, it's quite hard to top him when it comes to series villains. Dexter Morgan himself, being one of the smartest and most capable characters in the show, makes everyone else look less terrifying. Still, every story needs a villain of some sort. While some don't hold a candle to Dexter's bloodlust and discretion, others have made up for it in showmanship.