Villains: how are they created?

How are villains created? How does an author decide on how this villain inflicts pain, murder and fear? What makes this villain dangerous and just what are the villain's worst qualities? How does the main character deal with this villain and is it someone he/ she knows,had an issue with at some time or someone in it for the fun of killing and instilling fear? Join me for this great interview. Fran Lewis jua