Avatar: The Last Airbender is an animated series that premiered on Nickelodeon
on February 21, 2005. It's set in a world largely based on Chinese
mythology and tradition, though also quite different from the world we know. There are four nations: The Fire Nation, the Air Nomads, the Water Tribes, and the Earth Kingdom. In each culture, there are some people who can manipulate their nation's natural element: firebenders, airbenders, waterbenders, and earthbenders. One person, known as the Avatar, is capable of mastering all four elements. He (or she) is the spirit of the planet itself, a bridge between the physical world and the spirit world, and s/he is responsible for maintaining the balance of nature, and the balance of power between the four nations. The Avatar is reborn in an endless cycle, going back thousands of years.
When Avatar Roku of the Fire Nation died, the Avatar was reborn into an Air Nomad named Aang. When Aang was 12 years old, and nearing the completion of his airbending training under Monk Gyatso, he was informed that he was the Avatar, which he wasn't happy about. So he disappeared. In his absence, Fire Lord Sozin started a war of conquest against the other three nations, harnessing the power of a comet to greatly increase the firebenders' strength. The Air Nomads were all apparently wiped out.
The series begins 100 years later, when a 14-year-old waterbender named Katara, and her 15-year-old brother Sokka, of the Southern Water Tribe, discovered Aang frozen in an iceberg, where he'd been for a century. He was surprised to learn how long he'd been frozen, and they were surprised to learn he was an airbender- and the Avatar! The three of them set off on a journey toward the North Pole, hoping to find a master waterbender in the Northern Water Tribe to train both Katara and Aang. They travelled on Aang's 10-ton, 6-legged, flying bison, Appa, who had been frozen with Aang in the iceberg. They soon also acquired another companion, a winged lemur, who Aang named Momo. (There are many strange animals in this series.)
Along the way, they'd often clash with a 16-year-old exiled firebender, Prince Zuko (son of Ozai, the current Fire Lord). He was desperate to restore his honor and be allowed to return home, which he could only do by capturing the Avatar. Zuko travelled with and was trained by his uncle, General Iroh. Zuko and Aang both occasionally clashed with Admiral (nee Commander) Zhao of the Fire Nation.
The series' seasons are called Books. In Book Two, Ozai sends his 15-year-old daughter Azula, a firebending prodigy, to hunt down both the Avatar and her brother Zuko and uncle Iroh. She was joined by her friends Mai and Ty Lee, not firebenders, but each skilled fighters, in their own ways. Meanwhile, Aang gained another ally, a 12-year-old blind earthbender named Toph.
In each book, Aang must learn a new element, finally mastering all four before fighting Fire Lord Ozai and hopefully ending the war that began 100 years ago. And while each element normally requires years of training to master, he must master all of them before the summer's end, when Sozin's Comet will return.
Aang: Zach Tyler
Katara: Mae Whitman
Sokka: Jack De Sena
Appa & Momo: Dee Bradley Baker
Prince Zuko: Dante Basco
Uncle Iroh: Mako
Admiral Zhao: Jason Isaacs
Fire Lord Ozai: Mark Hamill
Princess Azula: Grey DeLisle
Toph: Jessie Flower
Mai: Cricket Leigh
Ty Lee: Olivia Hack
Monk Gyatso: Sab Shimono
Avatar Roku: James Garrett