Azula

Azula is the princess of the Fire Nation, daughter of Fire Lord Ozai and Princess Ursa, and the younger sister and archenemy to Prince Zuko. She was a key enemy of Team Avatar, chasing Avatar Aang and her banished brother far across the Earth Kingdom accompanied by her two best "friends" Mai and Ty Lee.

A Firebending prodigy, Azula is sadistic, manipulative and obsessed with power. She is a skilled tactician who orchestrated the Fire Nation victory over the Earth Kingdom capital Ba Sing Se and halted the invasion on Day of Black Sun.

Azula harbored deep mental instabilities, believing her mother favored Zuko over her. Raised by her father in an environment devoid of a mother-figure, Azula had to be nothing less than perfect in her father's eyes. After the betrayal of her two closest friends Mai and Ty Lee, these instabilities were brought up to the surface. Upon the arrival of Sozin's Comet, Azula was soon to be crowned Fire Lord; however, her defeat at the hands of her brother Zuko and Katara caused her to suffer a complete mental breakdown.