Come to the dark side, Luke- Olivia McCrary

There isn't really an universal definition of good or evil. People have attempted to decide what is right and what is wrong, but, nonetheless, standards have been different throughout history and between cultures. Evil is often defined as harming others, and good as helping others. But, if this understanding of good and evil was different, we might live in a society where things like cheating and lying are considered perfectly acceptable. Basically, everyone has their own unique ideas of what good and evil mean.
The concepts of hero and villain and of good vs. evil are never going to be easy to understand because they often very subjective. In movies, for example, sometimes the heroes use just as much violence to get what they want as the villains do. The violence caused by the hero is not seen as wrong because they are the "hero". When they kill a bad guy, everyone applauds their action. Yet, when the villain kills a good guy, what they did is viewed as a malicious crime. They have both done the exact same thing. What defines which person is the hero and which is the villain? It is really all about perspective. 
Personally, I don't think people are either completely good or completely evil. Some people are a combination of both, and some people do what seems evil or wrong in order to do something good. Because of this, people can't really be labeled "good" or "evil". Even the most selfless and honorable of people have lied and made selfish choices at some point in time.