A young boy named Wan from the Fire Lion Turtle took the ability to use firebending. He came across spirits who were once against humans. Wan came across Raava and Vaatu and split them apart. Their split made Vaatu control the spirits and attack the humans. To defeat Vaatu, Wan fused with Raava so Wan can learn water, earth and airbending. He uses these abilities to seal Vaatu and the Spirit World. At the end of his life, Wan's spirit reincarnated in various peoples as the Avatar. About 9 millennia later, Sozin of the Fire Nation planned to attack the Water, Earth and Air Nations. Aang (The current Avatar) was sealed up in an iceberg and found by Katara and Sokka to defeat the Fire Nation.