A century prior to the series' opening, Aang, a 12-year-old Airbender of the Air Nomad's Southern Air Temple, learned from his monk instructors that he was the Avatar. Usually, the Avatar is told of his true identity only after turning sixteen; however, the head monks feared that a war between the four nations was on the horizon, and that the Avatar would soon be needed to help maintain balance. Shortly thereafter, it was decided that Aang would be separated from his guardian, Monk Gyatso, and sent to the Eastern Air Temple to finish his training.
Confused, frightened, and overwhelmed by all that was happening, Aang fled from his home on his Flying Bison Appa. While over the ocean, a sudden storm caused Appa to plunge deep into the sea. Unknowingly entering the Avatar State, Aang used Airbending to put himself and Appa into an air bubble. The air bubble quickly froze into a sphere of ice, putting them both into a state of suspended animation.
When the series opens one hundred years later, the Fire Nation is on the brink of victory in its imperialist war. The Water Tribes are in crisis — the Southern Water Tribe's warriors have gone off to war, leaving their home defenseless, and the Northern Water Tribe, though largely intact, is continually on the defensive. The vast Earth Kingdom is now the only true barrier to the Fire Nation's domination, but as the Fire Nation continues to encroach on its borders and conquer its territories, hopes for victory grow bleaker with each passing year.
Aang (VA: Zach Tyler Eisen)
is the fun-loving, 112-year-old protagonist of the series, who is biologically 12 years old but was frozen in an iceberg for 100 years. He is the current incarnation of the Avatar, the spirit of the planet in human form. Aang is a reluctant hero, who would prefer adventure over his job as the Avatar and making friends over fighting the Fire Nation.
Katara (VA: Mae Whitman)
is a 14-year-old female Waterbender of the Southern Water Tribe. Katara discovers and frees Aang from an iceberg in which he had been trapped for one hundred years. With her brother Sokka, she accompanies Aang on his quest to defeat the Fire Lord, and eventually becomes his Waterbending teacher. In the original unaired pilot episode, Katara's name was Kya; this later is implied to be her mother's name.
Sokka (VA: Jack DeSena)
is a 15-year-old warrior of the Southern Water Tribe. With his sister Katara, he accompanies Aang on his quest to defeat the Fire Lord. The joker of the group, Sokka describes himself as "meat-loving" and "sarcastic". Unlike his companions, Sokka cannot bend an element, but the series, though it often makes him the victim of comedy at his expense, frequently grants him opportunities to use his ingenuity and weapons, including his trusty boomerang and a sword he forged from a meteorite.
Toph Bei Fong (VA: Jessie Flower)
is a 12-year-old blind Earthbender. In the second season of the show, she leaves her wealthy family and comfortable home to join Aang on his quest, with a plan to teach him Earthbending. Though blind, Toph "sees" by feeling the vibrations in the ground through her feet. She is the only Earthbender seen in the show to learn to bend metal and is considered one of the most powerful Earthbenders.
Zuko (VA: Dante Basco)
is the 16-year-old exiled prince of the Fire Nation and original antagonist of the series. Due to events in Zuko's past, his father, Fire Lord Ozai, deems him a complete failure, and Zuko feels he must capture the Avatar to regain his honor. Over time, Zuko struggles to deal with his anger, self-pity, and familial relationships; meanwhile, he grows sympathetic to the peoples his nation has terrorized. In Book Three, he defects from the Fire Nation, and joins Aang and the team in order to teach Aang Firebending. At the end of the series, he is crowned ruler of the Fire Nation.
Azula (VA: Grey DeLisle)
is the 14-year-old princess of the Fire Nation. She is Zuko's younger sister and one of the major antagonists of the series. Azula is a Firebending prodigy and is one of the few living Firebenders capable of summoning lightning. She has no qualms about bullying and threatening her relatives, reserving any familial loyalty for her father. She is first introduced at the end of Book 1, although she appears in the background in an earlier episode.
Iroh (Mako in Books 1 and 2, Greg Baldwin in Book 3)
is a retired Fire Nation general, known as the Dragon of the West, and Prince Zuko's uncle and mentor. Iroh was the original heir to the Fire Nation throne until his brother usurped the throne after Fire Lord Azulon's death. On the surface, Iroh is a cheerful, kind, and optimistically eccentric old man, but he still remains a competent warrior and a devoted surrogate parent to Zuko. Iroh is a Grand Master of the Order of the White Lotus, a secret society of men from all nations and helps retake Ba Sing Se during the series finale. Unlike most Firebenders, Iroh does not use fury as the source of his strength; instead he uses the original Firebending skills learned from the Dragons. He too is one of the few Firebenders with the rare ability to shoot lightning. He also has a unique ability to see characters of the spirit world.
One hundred years before the start of the series, a 12 year old Airbender Aang learns that he is the new Avatar. Fearful of the heavy responsibilities of stopping an impending world war and with the impending separation from his mentor Monk Gyatso, Aang flees from home on his flying bison Appa. During a fierce storm, they crash into the ocean, and Aang's Avatar state freezes them in a state of suspended animation inside an iceberg.
Aang and Appa are awoken a hundred years later by two siblings of Southern Water Tribe origin, Katara and Sokka. Aang learns that the Fire Nation started a war a hundred years ago, just after his disappearance. The Fire Nation's opening move in its campaign for global conquest was to launch a genocidal attack on the Air Nomads which drove Aang's entire race to extinction, thus making him "the last Airbender" left alive. He realizes that he must fulfill his destiny of becoming the Avatar and return balance to the world by defeating the Fire Nation. Aang sets out to master the three unlearned elements: Water, Earth, and Fire. With Katara and Sokka, Aang decides to head first to the North Pole to find a Waterbending master.
Aang soon discovers that Sozin's Comet, which Fire Lord Sozin used as a power supply to start the war, will return in the coming summer, giving the Fire Nation enough power to ultimately accomplish victory. Aang realizes that he must master all four elements and end the war before this time. For most of their journey to the North Pole, the group is pursued by Zuko, a banished Fire Nation prince and son of Fire Lord Ozai who is obsessed with capturing Aang to restore his lost honor.
After leaving the North Pole and mastering Waterbending, Aang travels to the Earth Kingdom to master Earthbending. There, the group meets Toph, a blind Earthbending prodigy who becomes Aang's second teacher. The heroes discover information about an upcoming solar eclipse which would leave the Fire Nation powerless and open to invasion. They struggle to reach the Earth King with this vital information, but are detoured by Appa's kidnapping. The psychologically self-tormented Zuko, his sister Azula, and her two friends Mai and Ty Lee chase the group as the struggle to reach Ba Sing Se. Azula engineers a coup from within that topples the Earth King and destroys any hope of a large-scale invasion of the Fire Nation.
The group recovers from the fall of Ba Sing Se, and travel to the planned invasion site. On the day of the solar eclipse, Aang's group and a smaller band of warriors launch a smaller invasion, which ultimately fails. Zuko confronts his father and defects from the Fire Nation. After a series of events, he manages to gain the trust of the protagonists and becomes Aang's firebending teacher. Aang and Zuko unlock the firebending secrets of the "Sun Warriors", Sokka and Zuko later travel to a Fire Nation prison to rescue Sokka's father and Suki, a warrior from Kyoshi Island.
On the day of Sozin's Comet, Fire Lord Ozai harnesses the comet's power to start a genocidal campaign to destroy the rest of the world. Aang and his friends face the self-proclaimed "Phoenix King" Ozai, Azula (now crowned as the new Fire Lord by "Phoenix King" Ozai), and the Fire Nation army. Aang confronts and defeats Ozai. At the same time, Zuko is incapacitated by Azula, who is then defeated by Katara. Also, the Order of the White Lotus takes back Ba Sing Se from the Fire Nation. Zuko then becomes the new Fire Lord and promises to help re-build the world alongside Aang.