Eighty two years before Avatar Aang’s birth, the Avatar before him Roku was born. He was born and became friends with Prince Sozin, they had the same birthdays and always celebrate them together. They were best friends until their 16th birthday when Roku was named Avatar by the Firesages. Once he had the title Avatar he had to leave home to go master the elements. A few years later Sozin became the Firelord. Twelve years after leaving his country for his Avatar journey, Roku has become a fully-realized Avatar. He returned to the Fire Nation to reunite with his friend Sozin, who has since become Fire Lord. Roku winds up marrying his childhood sweetheart, Ta Min, with Sozin taking the position of his best man. At the wedding, Sozin asks to speak with Roku in private. He begins telling Roku that he has been thinking hard about the state of the world, and that the Fire Nation is going through a period of great prosperity. He proposes to Roku that together, the two of them could spread this wealth to the world by expanding the empire. Roku is horrified by this proposition, and tells Sozin that the Four Nations are meant to be kept separate and that he should not think of this again. In the following years, Roku and Ta Min had a child, though nothing else about this child is revealed.
At least twenty years later, however, Roku discovers that Sozin has gone ahead with his plan, and set up colonies in the Earth Kingdom. He confronts his old friend, and commands him to stop his aggression, which Sozin replies that loyalty lies with him and the Fire Nation. When Roku declines this, it leads Sozin to attack him. The two engage in a battle, with Roku easily overpowering his old friend and finally destroying most of the palace and defeating Sozin. He decides to spare Sozin's life for the sake of their past friendship, but not before warning him never to move forward with his plans again, or it would result in his own defeat.
Twenty-five years later, Roku's home island is consumed in a volcanic eruption so massive that Fire Lord Sozin could see and feel it from a hundred miles away at the palace. Roku attempts to contain the volcanic destruction, using his Bending and even going into the Avatar State; however, the awesome power of the volcano proves to be too powerful, even for the Avatar. At that moment, Sozin flies in on his dragon to assist his old friend. The two use their Bending to try to contain the lava flow, but are hindered by poisonous gases, which eventually overwhelm Roku, leaving him lying on the ground and begging for his old friend's help. Sozin suddenly realizes, however, that Roku's death would allow him to fulfill his plans, and leaves his old friend to die along with his dragon Fang, who curls up with Roku as he is engulfed in a pyroclastic flow.
Twelve years later, Sozin begins The War. Sozin uses the power from the comet to wipe at all the Air nomads knowing that the next Avatar would be born into the Air colonies. Within the twelve years it took for Sozin’s siege to be pulled off Aang was able to master Airbending. Since the Air nomads foresaw the siege the Firelord Sozin was planning they deiced to tell Aang he was the Avatar four years ahead of time. When they told Aang that he was the Avatar and couldn’t have a normal life he ran away on Apa. He was caught in a storm around the southern water tribe. The storm throw Apa into the water almost causing them to drown. Aang went into the Avatar state for the first time and made a air bubble for him and Apa. They sank until the bubble froze. Aang was frozen for a hundred until two southern water tribe teens found him while searching for food. Aang went on to learn all the elements with Katara and Sokka. Aang realized that all the air nomads where killed and that the fire nation started a war.
Aang and his team were able to defeat the Firelord, and Zuko, son of Ozai, took the throne. The world was peaceful. Aang and Katara had a son, ‘Tenzin’ who was able to Airbend. Sokka and Suki had a son that had daughter named ‘Korra’ who was born after Aang’s death. She was the new Avatar, she was a born in the southern water tribe mastering water bending along with all the other new waterbenders that moved there from the northern water tribe. Korra lived a peaceful life mastering all the elements.
Zuko and Mai had two son’s. The older brother took the throne while the younger brother left to live somewhere on the outskirts of the fire nation. The new Firelord didn’t have any children living the throne open since the younger brother never came back. The younger brother had a son. The son was always furious that his father never took the throne and how he could never have it now. After his fathers passing he came out and said that he was next in line to become to the Phoenix King after his great grandfather Ozai.
Korra was 99 when she was assassinated by a mysterious group. The new Avatar 'Chen Dilong' was born in the Earth Kingdom. When he turned sixteen he was named the new Avatar. When he was 41 he entered the spirt world to get information about the people who assassinated Korra. Once he had the information about the mysterious group he returned to his body, but when Chen got there his body was missing. Chen was now lost in the spirt world until he could find his body.
The Earth Kingdom found out about there missing Avatar, and immediately blamed the Water Tribe. They thought they wanted revenge for their Avatar who was murdered. The Water Tribe told the Earth Kingdom that it was the Fire Nation who killed him so they could get their Avatar next. The Fire Nation was upset that they were being accused of starting another war and join with the Earth Kingdom and blamed the Water tribe. Air Nomads heard about the argument between the the nations and then agreed with the Water tribe that the Fire Nation murdered the Avatar to make the cycle move faster.