Ozai
When Sozin's Comet arrives he dubs himself the Phoenix King and declares that he is the ruler of the world. He also appoints his daughter Azula to the rank of Fire Lord. While attacking the Earth Kingdom, he is confronted by Avatar Aang.  Because of his enhanced power and Aang's refusal to kill Ozai, he originally has the advantage.  He is eventually defeated when Aang enters the Avatar state and strips Ozai of his Firebending ability by Energybending. After the defeat Team Avatar taunts him and calls him names, stating that he's not so tough now without his power. He is then imprisoned in the Fire Nation prison where Zuko visits him, stating that maybe prison will set him up in the right path, then demands to know where his mother is.