How To Create A Believable Villain

Creating a believable, three-dimensional villain is probably the hardest thing a writer has to do. The mistake most new writers make is to create a villain that is so evil, they are totally unbelievable. So what’s the secret? Quite simple - to create a real villain you first have to make them nice. Confused? Please read on and hopefully the tips I’ve learned over the years will make sense.
The first thing I do when creating my villain or antagonist is to give them a back story. I create a detailed background for that person. What are their passions? What are their hobbies? With hobbies, I find the stranger the better. For example,  your villain could commit a heinous act in the morning followed by a piano lesson in the afternoon. What was their childhood like? The latter I found was the key to discovering what made them into the ghastly character they are today? What was the pivotal moment they turned their back on society? You also need to explore their weaknesses, everyone has them, and this can be used as leverage for the protagonist later on in your story.
Although the villain does need to have weaknesses, you must ensure they can outwit the hero in your story. It is key to remember that the villain lacks morals and so, therefore, will always win until of the end of your story. This builds tension and keeps the story moving. How quickly would a hero defeat a stupid hero; there is no challenge and makes for quite a weak plot.
What is your villain’s motivation? Power? Greed? Revenge? The villain's actions, although dreadful, must be to some degree understandable. We have all read news reports of killers that the neighbourhood thought were ‘normal’. Research villains in movies or in real life and you will discover the villain believed their actions were justified.
Make your villain different shades of gray, not just black and white. They must have likeable characteristics. Are they witty? (Die Hard) Are they kind to the elderly? (Psycho!) Do they have a little puppy they dote on? (Silence Of The Lambs) This will increase the reader’s attention to the plot and will make the story more realistic.
Give the villain and hero a connection somehow. Did the hero do the villain an injustice long ago and now the villain wants revenge? A great example of this is Cape Fear. Are they related and the hero was the parents’ favourite and the villain carries a deep seated resentment for being the social outcast? If possible, give them a similar background. The hero and villain must understand each other’s weaknesses for the battle between them to be realistic. That means there must be a certain similarity.
Lastly, do your research. If your villain is a religious fanatic, watch documentaries and read news articles on the subject until you know your villain inside out. What are their mannerisms and speech patterns?  The same rule goes for any villain. For them to be realistic and believable, you must study the real thing in depth. We all remember the chilling interview and court appearance of Ted Bundy.
Put simply, writing a villain is almost identical to writing any other character: give the character a personality, a back story, and a motivation. That's it. Remember they must be a person first, a villain second.