A drama is considered a tragedy when its main characters are noble and the outcome is fatal. The main character makes a fatal error (Hamartia in Greek as defined by Aristotle) trying to do the right thing in a scenario where the right thing cannot be done. This leads to the main character's death or other form of moral or physical corruption, such as going crazy. In the case of Hamlet, prince of Denmark, the main character tries to avenge the death of his father the king by killing his murderer, the king's brother Claudio, who did so and married Hamlet's mother the queen to become king.
