Film study

1 or 2 weeks ago during English class we watched a movie called Dragonheart, the movie was about a knight named Bowen. Bowen tried to hunt every dragon down believing that his student Einon was over taken by having a dragon's heart inside him.
However trying to find every single dragon he came across the dragon. The dragon tells Bowen it wasn't the dragon's heart that corrupted him, it was him self changing.