Aang (Zach Tyler Eisen) is the 12-year-old protagonist of the series who had been frozen in ice with his flying bison, Appa, for 100 years. He was find by a young Waterbender named Katara who later becomes his love interest. He is the current incarnation of the Avatar, the master of 4 elements. Aang is a reluctant hero trying to return balance to the world.
Katara (Mae Whitman) is a 14-year-old Waterbender of the Southern Water Tribe. Katara and her brother, Sokka, discover and free Aang from a block of ice in which he had been frozen for 100 years. With her brother Sokka, she accompanies Aang on his quest to defeat the Fire Lord Ozai and, eventually, becomes his Waterbending teacher. Katara is also one of the only Waterbenders that have the ability to Bloodbend, which allows her to control any person by bending the water inside the blood; although she is reluctant to use the ability. In the original un-aired pilot episode, Katara's name was Kaya; this later is stated to be her mother's name.
Sokka (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. As both the joker and the idea man of the group, Sokka describes himself as "meat-loving" and "sarcastic". Unlike his companions, Sokka does not have any bending ability; however 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. From creator Michael Dante DiMartino it was revealed that Sokka also had some waterbending potential, but never realized it.
Toph (Jessie Flower) is a 12-year-old blind, member of the rich family of Bei Fong, tough Earthbender who first appears in the second season of the show. Not long after meeting Aang and his friends, she leaves her wealthy family and comfortable home to join Aang on his quest and a plan to teach him Earthbending. Though blind, Toph "sees" by feeling vibrations in the ground through her feet. She is the only Earthbender to learn to bend metal and is considered one of the most powerful Earthbenders.
Zuko (Dante Basco) is the 16-year-old exiled prince of the Fire Nation and original antagonist of the series, including the end of the . 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 complex familial relationships. Over the course of the series he grows sympathetic to the people his nation has terrorized. He takes on the identity of "the blue spirit" at the end of season one and beginning of season two. In season three, he defects from the Fire Nation and joins the Avatar and the team in order to teach Aang Firebending. At the end of the series, he is crowned ruler of the Fire Nation.
Azula (Grey DeLisle) is the manipulative 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 casting lightning. She uses fear to control her relatives or friends Mai and Ty Lee, reserving her family loyalty for her father alone.
Iroh (Mako in season one and two. Greg Baldwin in season three) 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, optimistically eccentric tea-loving old man, but he still remains a powerful 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 anger as the source of his strength; instead he uses the original Firebending skills learned from the Dragons.
The characters of "Avatar: The Last Airbender" were designed by Michael Dante DiMartino and Bryan Konietzko, the co-creators of the series. The anime-styled character art based on Shinichiro Watanabe's "Cowboy Bebop", "Samurai Champloo", and "FLCL" ("Fooly Cooly") of Gainax. The original character conception was derived from a sketch by Bryan Konietzko that depicted a middle-aged balding man with an arrow on his head. Studios such as Studio 4°C, Production I.G, and Studio Ghibli, which produced anime-styled cartoons, were also sources of inspiration.
The greatest influences on the series were Asian art and history; the characters' various personalities and traits are based on philosophical teachings such as Taoism and Buddhism. In the show, some characters have the ability to manipulate one of the four classic elements of ancient philosophy: Water, Earth, Fire and Air, although the Avatar has the ability to control all four. Each of these employ a different form of martial arts in their fighting choreography: Ba Gua for Airbending, Hung Gar for Earthbending, Northern Shaolin for Firebending, and Tai Chi for Waterbending.<ref name="avatar2/index.jhtml"></ref> These individual styles of martial arts also reflect on the personalities of the user and the nations as a whole. These starkly individual tendencies are explained in eighty-five distinct types of "Jings", or internal energy. For example, Ba Gua employs the "negative jing" to create erratic circular movements and capitalizes on centripetal force and defensive positions while Northern Shaolin follows the "positive jing" and emphasizes brute strength and aggression to generate power. The negative jing reflects Aang's bending styles and his tendency to be unpredictable and extremely carefree, as well as his pacifist and non-aggressive nature.
Many of the recurring characters of the series have received more depth in their personalities, which are usually based on their respective element. Aang, a pacifist monk, is also very carefree and childlike, which is commonly attributed to the "freedom" of the wind and the air. Toph, despite being blind, is extremely perceptive of the world around her due to her connection to the Earth. Unlike Aang, she is extremely brusque when criticizing others, which is attributed to Earth's tough and unbreakable nature.
The characters of "Avatar: The Last Airbender" received both praise and criticism from reviewers. Troy Island Mell, of IGN, felt that the story "would [not] be anywhere near as good as it is without its ability to create such strong characters". In particular, Mell enjoyed the development of Katara and Zuko throughout the first season, but thought that Zuko's relationship with his uncle was not "very organic." Jamie S. Rich of DVD Talk generally agreed with Mell's assessment of the characters. Rich also praised the fact that, unlike many cartoon television series, "Avatar" introduces antagonists that have a deep backstory and "are [not] just evil for the sake of it".