Avatar: The Last Airbender, also known as Avatar: The Legend of Aang in some regions, 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 a largely Asian-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 follows 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. The series also follows 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, with various other influences from different East Asian, Southeast Asian, South Asian, North Asian, and Native American cultures.

Avatar: The Last Airbender was a ratings success and received widespread acclaim from critics and audiences, with high praise for its characters, cultural references, art direction, voice acting, soundtrack, humor, ending, and thematic content. The series' themes include concepts rarely touched on in youth entertainment, including war, genocide, sexism and gender roles, imperialism, totalitarianism, class warfare, political corruption, indoctrination, animal cruelty, and free choice. It won five Annie Awards, a Genesis Award, a Primetime Emmy Award, a Kids' Choice Award, and a Peabody Award. Since its release, the show has been regarded by critics as one of the most acclaimed series of the 21st century, and one of the greatest animated television series of all time.

Avatar aired on Nickelodeon for three seasons, from February 2005 to July 2008. The extended Avatar franchise includes an ongoing comics series, a prequel novel series, an animated sequel series, and a live-action film, as well as a live-action remake series produced for Netflix. The complete series was released on Blu-ray in June 2018 in honor of the tenth anniversary of its finale and was made available to stream on Netflix in the United States and Canada in May 2020, on Paramount+ in June 2020, and on Amazon Prime Video in January 2021.