Zuko

Fire Lord Zuko was a skilled and powerful Firebender, born as a prince in the Fire Nation royal family. His story often paralleled that of the Avatar, Aang. Initially the main antagonist, Zuko's life revolved around trying to capture the long-lost Avatar to end his banishment and to regain his honor as Crown Prince of the Fire Nation.

With support from his uncle, Iroh, and after much internal struggle and turmoil, Zuko rejected Ozai's Fire Nation and joined the Avatar's group to become Aang's friend and his Firebending teacher in an effort to restore his as well as the Fire Nation's honor.

While Aang defeated Ozai, Zuko, with the help of Katara, defeated his prodigious younger sister Princess Azula and took his place as Fire Lord, declaring the end of the War and the start of an era of love and peace.

Ultima role
Zuko somehow appeared as one of Marlon's companion for getting the Ultimacrystal to destroy the Orgs himself.

in some occasional reason, Zuko may be only the few of Society member(beside Kevin including Ty lee and Mai) whom still care for her sister, Azula, even she obvious just going to kill him anyway due to the fact he and Katara defeated her.