Azula

Azula was the princess of the Fire Nation Royal Family, and younger sister of Zuko. Azula believed Zuko to be their mother's favorite, so she always strived for greatness. She became vindictive, sadistic, and cold over the years and became obsessed with gaining power and recognizition from her father. When she heard that the Avatar was alive, she went on a search to look for him with her two best friends, Mai and Ty Lee.