Macbeth is a Scottish nobleman who is a great military leader. One day, three witches prophesy to him that he will become the Thane of Cawdor and then King of Scotland. When he becomes Thane of Cawdor, Macbeth decides the prophecy must be true.
This makes him ambitious and impatient. With a great deal of encouragement from his wife, he kills the current king so that he may take the throne himself. He also kills various other people who might, he fears, be contenders for the throne.
As king, he rules poorly. Because of this, various nobles work together to overthrow him (by killing him in battle) and put the son of the previous king on the throne.
Really good answer! Thanks! I'm writing about Macbeth and this really helped me.