Aang is the main character of Animal Crossing's Avatar: The Last Airbender. He is the first chaater you meet. He in one of the few humans in the game. His pet is Momo.
Aang is the Avatar and the Fire Nation want him. More info here. 
The whole game is about helping Aang as much as possible. In order get the Airbender Tattoo you must do all of his quests. You can fight him in the Western Air Temple. He is a villager in an Airbender town. If you are an Airbender he will teach you.
The only way to defeat him is to team up with him whilst fighting Oazi, then betray him. It is impossible to defeat him anywhere else.
Aang chose four toys out of thousands -- a turtle shell rattle (Water), a string-powered propeller (Air), a Hog Monkey (Earth) and a drum (Fire). These four toys were the same ones that past Avatars had chosen for generations when they were children. This is the same procedure used by the Tibetan Buddhist monks to recognize the next reincarnation of the Tulku Lama. According to the book Magic and Mystery in Tibet by Alexandra David-Néel, "a number of objects such as rosaries, ritualistic implements, books, tea-cups, etc., are placed together, and the child must pick out those which belonged to the late Tulku, thus showing that he recognizes the things which were his in his previous life". After the end of Book 2 (Earth), Aang's voice starts to get deeper as Book 3 (Fire) progresses. This shows how Aang matures throughout the third season. Aang has been called several names including "Twinkle Toes" (by Toph), "Guru Goody-goody" (by Zuko), "Aangy" (by some of the young girls of Kyoshi Island) and once been called "Colony Trash" (by a bully, Hide). Aang appears to be the youngest monk ever to master Airbending, receiving his tattoos, the Air Nomads' sign of Airbending mastery, when he was still a child. This is most likely because he is the Avatar. However, since there is no evidence of how young most Air Nomad Avatars were when they mastered Airbending, we can only assume Aang is the youngest Monk and Air Nomad Avatar to receive his tattoos. According to Avatar Extras, Aang had to master 36 complex Airbending forms to master Airbending, and he had learned only 35 of them, but was given the rank of master when he created the air scooter technique. Aang is portrayed by Noah Ringer in The Last Airbender movie. Aang is the only known male Airbender to grow a full head of hair, although that happened because he was unconscious and couldn't shave his head. It was widely speculated that Aang being a "Fully Realized Avatar" required him to master all the elements, or be able to bend all at once with at least some amount of skill. Avatar Extras explained that being a fully realized Avatar means that the Avatar in question is able to control himself/herself whilst in the Avatar State. Doing so grants the Avatar all the power and knowledge of their past lives. In the final episode, Sozin's Comet, Part 4: Avatar Aang, Aang is seen to be wearing a necklace similar to the one that was on Gyatso's skeleton in the episode The Southern Air Temple. However they are probably not the same ones. In the movie the necklace that Gyatso wears was originally made by Aang. The name Aang is similar to the Malaysian word "angin," meaning "wind." Aang is also the Inuit word for "hello," which could be a reference to his friendly nature.