Aang: Because I never wanted to be.
Avatar: The Last Airbender is an animated series that ran from 2005-2008; also known as Avatar: The Legend of Aang in some countries, and is the 20th series in Nickelodeon's popular brand of original cartoons, known as Nicktoons. Avatar is the first series in an eponymous franchise which takes place in a Constructed World divided into four nations: the Water Tribes, the Earth Kingdom, the Fire Nation, and the Air Nomads. Each nation has developed a spiritual art form to manipulate ("bend") their namesake element, but only the Avatar — one person reincarnated periodically into each race — is capable of mastering all four elements. The Avatar's role is to serve as a peacekeeper and protector for all four nations (as well as bridging and balancing the physical and spiritual worlds).
The show's story centers around Aang, the twelve-year old (chronologically 112) incarnation of the current Avatar and the eponymous last airbender. He must master the four bending arts so that he can save the world from Fire Lord Ozai and end the century-long war, a war which he accidentally avoided, spending a hundred years trapped in an iceberg after running away from his sudden heavy responsibility as the Avatar. Ozai's plans for domination are on a specific timetable, though, meaning that Aang has until the end of summer to stop them.
Aang has thankfully found himself in good company with teenage waterbender Katara and her brother Sokka, the two who freed Aang from the iceberg. As the trio works to save the four nations with the company of Aang's lemur and flying bison, they gain many more allies; take a look at the Character Sheet to get to know more about the cast.
There was a canonical online game, Escape from the Spirit World, released between seasons two and three and set between them.
The first season was adapted into a live-action film directed by M. Night Shyamalan — The Last Airbender — which is the second Shyamalan film to be inspired by a Nickelodeon show. The film was intended to be the first season in movie form, with the hope that a pair of sequels based on the other two seasons would follow. The film's critical failure, however, put a stop to any further plans for any follow-up to the show.
A Sequel Series, The Legend of Korra, premiered in 2012. The new series takes place seventy years after Avatar and focuses on the next Avatar, a hotheaded waterbender named Korra, who has to live up to her responsibilities as the Avatar in a world that is vastly different than it was in Aang's time.
Nickelodeon has also released a digest graphic novel called The Lost Adventures, which includes the out of print Expanded Universe strips. Several graphic novel trilogies written by Gene Luen Yang and drawn by Gurihiru have been released that detail the Gaang's rebuilding of the world and serve as a bridge to Korra. The first was called The Promise, and picked up immediately after the end of the series. The second trilogy was called The Search and was notable for finally revealing the fate of Zuko's mother, which was one of the biggest loose threads of the original series. The Rift was third in the series, Smoke and Shadow is the fourth and North and South is the fifth and final to be penned by Yang. A new graphic novel series titled Imbalance will be released in 2018 and 2019 with Faith Erin Hicks writing and Peter Wartman on art. All of these projects are being published by Dark Horse Comics.
On September 18th, 2018, Netflix and Nickelodeon announced they will be doing a live action television adaptation of the show, with DiMartino and Konietzko returning as showrunners and executive producers
This show is not to be confused with other meanings of the term "avatar".
Due to the sheer number of trope examples, they have been divided into their own alphabetized pages. There is also a largely-complete recap page available for those who want to see what all the fuss is about.