Who is the Avatar? And what was he trying to accomplish?

Avatar: The Last Airbender (abbreviated as ATLA[2]), also known as Avatar: The Legend of Aang in some regions or simply Avatar, is an American animated fantasy action television series created by Michael Dante DiMartino and Bryan Konietzko and produced by Nickelodeon Animation Studio.

Avatar is set in an Asiatic-inspired world in which some people can telekinetically manipulate one of the four elements—water, earth, fire or air—through practices known as "bending", inspired by Chinese martial arts. The only individual who can bend all four elements, the "Avatar", is responsible for maintaining harmony among the world's four nations, and serves as the link between the physical world and the spirit world. The series is centered around the journey of twelve-year-old Aang, the current Avatar and last survivor of his nation, the Air Nomads, along with his friends Katara, Sokka, and Toph, as they strive to end the Fire Nation's war against the other nations and defeat Fire Lord Ozai before he conquers the world. It also follows the story of Zuko—the exiled prince of the Fire Nation, seeking to restore his lost honor by capturing Aang, accompanied by his uncle Iroh—and later, his sister Azula. Avatar is presented in a style that combines anime with American cartoons and relies on the imagery of primarily Chinese culture,[3] with some other East Asian, Southeast Asian, South Asian, New World, Siberian, and Arctic influences.

In the show Avatar: The Last Airbender, Aang was the current Avatar and the last survivor of his nation, the Air Nomads. He and his friends Katara, Sokka, and Toph, strived to end the Fire Nation's war against the other nations and defeat Fire Lord Ozai before he conquered the world.