Avatar - The Legend of Aang

Avatar: The Last Airbender is an animated series created by Michael Dante DiMartino and Bryan Konietzko, for Nickelodeon.A series is set in a fictional world influenced by Asian martial arts, mixed with elemental spells. The adventures of Aang, the last successor of a long line of Avatars. He and his friends have a mission to save the world from the attacks of the Fire Nation, who wants to dominate the world.

About
In a lost age, humanity was divided into four nations: the Water Tribe the Earth Kingdom, the Fire Nation and Air Nomads Within each nation, there is an order of notable men and women, called " Folders, which are able to manipulate their native element in a kind of struggle, the Bender, which combines martial arts and magic. To maintain the balance between these nations, each generation is born a single Folder, which is able to control all the four elements. This Bender is the Avatar, a choice that expresses the spirit of the world in human form. When the Avatar dies, he is reincarnated in another nation, following an ancient cycle. Starting with the mastery of his native element, the Avatar will learn how to command all four elements. Throughout the ages, the countless incarnations of Avatar have served to keep the four nations in harmony.
Until then, the avatar disappears, just when the world needs him because only power that can stop the ruthless Fire Nation conquer the world.

But when the planet needs your presence, he disappears without a trace. When all seemed lost, two brothers of the Water Tribe boy rescues a stranger from the dangers of an iceberg and soon learn that the boy, who goes by the name of Aang, an Airbender is also, besides being the one who has the powers of the Avatar is long lost. Now is the time to Katara and Sakka help the young Aang to face his destiny and save the Water Tribe.

Ang ("Avatar")
In a flashback in "The Tempest" (the 12th of the season), the old monks of the Temple of the Southern Air meet with Aang and show that he is the reincarnation of the Avatar. Monk Gyatso, Aang's mentor, insists that it must be created as a normal child, but his colleagues reject interference and decided to send Aang to the Temple of the Eastern Air. Not wishing to be away from his mentor, and frightened by his new responsibilities, Aang flees the temple mounted on Appa, his Bison - Flying. In the first two episodes of the first season, we know that the two encountered a violent storm that threw them on the ocean floor. At that time, Aang entered the Avatar State for the first time, using the fold of air and water to protect Appa with a bubble of air frozen.
After one hundred years trapped inside an iceberg, Aang and Appa are released by Katara and her brother Sokka. It is the beginning of an endless sequence of adventures, in which the four characters start toward the Water Tribe North to find a master at bending water to Katara. Aang is the spirit of its previous incarnation, Avatar Roku, who informs him that he must learn to master all the elements and defeat the Fire Lord Ozai before the return of Sozin's Comet, in late summer. In the second season, Aang meets Toph Bei Fong, a blind girl who becomes his mistress into the fold of the earth. Some episodes later, Sokka discovers that a solar eclipse that will happen before the arrival of Sozin's Comet, which will leave the folders of fire without power. At the end of season two, Aang is involved in a battle in the underground caverns of Ba Sing Se. He is mortally wounded when struck by lightning from Azula, but is healed by Katara, using water from the Spiritual Oasis.
In season three, Aang and his friends have a new enemy - an assassin hired by Zuko, able to bend the fire with a third eye on his forehead. Despite the defeat of the Earth Kingdom's second season, Aang and his remaining allies invade the capital of the Fire Nation in the two-part episode "The Day of Black Sun," but his plan of attack is thwarted by Azula. In the next episode, Zuko is offered as a master of firebending to Aang, who accepts it with the suspicion of his friends.

Katara
Katara is a water bender who lived in the Water Tribe the South Pole until the day they met, along with his brother, the new Avatar, Aang, frozen in an iceberg. 
From this event, Katara was able to leave his small tribe and travel the world with Aang and Sokka, to help the Avatar in his quest to save the world and also in his own quest for a master waterbending . 
Katara is a friendly person and is concerned with the welfare of his friends. But this bender can also be very tough and difficult to face when you are nervous. She is determined enough and strives to be a bender getting better and to be able to help the Avatar.

Sokka
Sokka is a warrior of the Tribe's Water Polo South Along with his sister Katara, was responsible for his small tribe after the other warriors left for the war. It was also with her sister who found the new Avatar, Aang. 
One can say that Sokka is one of the most responsible for the comic series. It is impossible not to laugh at things that happen to him. The guy seems a magnet for stupid situations.

Toph
Toph is a great bender of land that appears only from the 6th episode of season 2 (The blind bandit), when with the group of Aang. 
Despite being blind, Toph is far from being a useless and fragile girl. As she said, although he was born blind, never had trouble seeing because with your feet can "see" anything around them. 
With his strong temperament, Toph does not take insult home and is always ready to stop anyone who bothers. Nevertheless ... or perhaps because of it, has become one of the most popular characters in the series.

Trivia
Meaning Avatar
Avatar, in Hinduism, is a manifestation of a body to be immortal, sometimes even the Supreme Being. From the Sanskrit avatara, which means "descent", usually denoting a (religion) incarnations of Vishnu (such as Krishna), which many Hindus revere as a deity. Many non-Hindus, by extension, use the term to denote the incarnations of deities in other religions.