Writing strong characters is one of the biggest challenges in writing any story. They need to be complex and believable, but they also need to make sense within the context of your story and your plot. One of the most difficult types of characters to do well are the villains, the bad guys of your story. When you build them well, they can definitely be some of the most interesting and fun characters you have to play with, but if they are done poorly, they can drag the entire story down. So, what can you do to avoid dull bad guys?
- What do they want?
What, in the context of your story, sets your villain on the opposite side of your hero? What are their goals, their motivation? Ideally, your bad guy's goals should be in direct opposition to your hero’s goals. By putting your hero and your villain in conflict, you justify the tension between them.
- Why do they want it?
Whatever it is that your villain wants, you should know why they want it. They should have a good reason for the actions that they take. Ideally, that reason should be logical and emotionally resonant. Avoid mustache-twirling. Villains who plan evil for evil’s sake are boring. The much more interesting villains are the ones who are the heroes of their own stories, the ones who can justify their actions within their own moral framework. It also makes it more interesting for the readers, who can understand the bad guy's point-of-view, why they are acting the way they are.
- What's their motivation, their inciting incident?
If you know what they want and why they want it, you should understand their deeper backstory and be able to tie those details in. The more impactful and emotional a villain's motivations are, the stronger they make the character. Most of us can think of a character whose actions seem justified when placed in the context of their history. Magneto in the X-Men series is set up as a villain, but as we explore his backstory we learn that his animosity towards humans looking to regulate mutants comes from his experiences during the Holocaust. So, when he says, "I've been at the mercy of men 'just following orders.' Never again," we understand his point of view. Hell, we can sympathize with it.
- How are they going to accomplish their goal?
Unless comedy is what your goal, your bad guys should be competent and smart. A bumbling villain who makes stupid mistakes is fine if you are setting him up as a comedic foil to your hero, but if the goal is genuine conflict and tension, your villain needs to be effective. The threat of the bad guy prevailing has to be credible. They don't need to be invincible, it's generally boring if they are, but they do need to provide a genuine challenge to the hero. There needs to be a sense on the audience's part that the bad guy might prevail, and the hero might fail.
Your villains should be dynamic and believable. They don't need to be likable or sympathetic, though they certainly can be. However, they do need to make sense within the context of your story. They need to provide a credible threat and have goals that, if not in direct opposition to your heroes, are at least different to those of the hero. When crafted well, the bad guys can make some of the best characters.