There are multiple ways of uncovering how a person can become a villain. I can look at my own life and see what others did to harm me or what I have done to them by preventing them from accomplishing what they wanted. I may think that is not like a villain because it wasn’t a horribly vicious thing. However, I assume that I deserve what is good more than others do and therefore justify my own bad behavior.
A wise person once pointed out to me that people who refuse to acknowledge their own shortcomings, become the cruelest when persecuting other people for their faults. Interestingly, we may criticize real people that perform the same corrupt actions as we do, but we will attach ourselves to fictional characters like ourselves. So the reader who constantly seeks villains who either want to rule or destroy the world may not be as common as writers assume.
Two of my favorite villains are Javert in Les Miserable in Les Miserable and Roger Chillingworth in The Scarlet Letter. Let us look more closely at the appeal of these literary villains. Javert assumed any effort to chase down a petty thief who had repaid society for his crime was justified. Chilllingworth secretly tormented the man who he assumed had seduced his wife when he had been absent for years himself. In both cases the villain never confessed to reveal their motive for persecuting the protagonist. But, their was no need to. Their crime was lack of compassion. They both thought they were justified in their pursuit of the protagonists, who had fallen down into the slippery slope of a bad situation..
That is actually the mark of an excellent writer—being able to produce villains who see themselves as right, and yet the audience sees through their façade and realizes their depravity. Sometimes, this is done by having the villain be insane. But, one must really understand mental illness for this character to ring true. It is more likely that a person who seems perfectly normal has decided on a course of action that is cruel to others with an ultimate cause that they rationalize as good. However, this ultimate cause is actually self-promotion.
How does a writer make a character seem villainous? Have them do selfish things that hurt other people and show that they simply don’t care about this at all. They might have the attitude that other people aren’t really important as they are and don’t matter. Therefore, these characters see committing destructive acts as being justified. The skillful author knows how to reveal that there is no actual justification for becoming evil.