I don't know if I would say that a person can be moral or immoral. Their actions and thoughts can be moral, but the person him/herself cannot be moral or immoral, they can only be a moral agent. Morality, or ethics, is a standard of behavior - principles of right action - based on reasoning and choices. Something can at the same time be subjectively moral and objectively immoral. We all make moral and immoral decisions, however, these individual decisions do not make us a good or bad person. So, can a good person create a "bad/evil" character? Sure. Can a bad/evil person create a "good" character? Absolutely.