Zuko

Son of Firelord Ozai and Ursa, Prince Zuko was banished from the Fire Nation for speaking out of turn in the royal warroom. For this he was forced into an Agni Kai with his father, who gave him a huge scar on the left side of his face as a reminder of his "shame". He was then banished with his wise uncle Iroh and would not be allowed home until he caught the Avatar, and thus return his honour. In season 2 Zuko and Iroh become fugitives. Whilst Iroh just wants to start a new peaceful life, Zuko still yoyos between good and bad. A new persona is borne of this inner conflict - the Blue Spirit. When it finally seems Zuko has changed for the better he throws it all away to return to the Fire Nation with his evil sister Azula and claim his throne once again. Season 3 sees Zuko still struggling between good and evil. Although he now has his throne back, he feels guilt and anger because it was through his fault that his uncle was thrown in prison. He eventually confronts his evil father and says that he is leaving to help the Avatar learn firebending. Ozai shoots lightening at his son, but through a lesson Iroh had taught him Zuko was able to redirect it. He escapes and follows Team Avatar to the Western Air Temple, where he offers to help teach Aang. Despite being ultimately rejected and attacked after his first attempt, the team eventually allows him to join, mostly thanks to Toph's support of him. However Katara doesn't trust him at all and at the end of "The Western Air Temple" gives Zuko a serious warning not to step out of line, or she will make sure his destiny ends permanently.