Avatar Yangchen was the Air NomadAvatar succeeding the unnamed fire Avatar and preceding Avatar Kuruk. A very respected figure, she was hailed for her wisdom, determination, and power. Although the Air Nomads were perceived to be pacifistic people, Yangchen was feared for her fierce willingness in doing whatever was required to perform her duties as the Avatar and maintain balance and peace throughout the world. Due to her devotion, no threats of war occurred for an entire generation after her death.
Yangchen was born and raised in the Western Air Temple. Like all Avatars, she mastered the four elements and the Avatar State in order to maintain world peace. Yangchen was a powerful bender and used aggression to accomplish her tasks as the Avatar, engendering some fear upon her peers. Nonetheless, she was quite respected and two statues were made of her: one in the Eastern Air Temple and one in the Western Air Temple. She died around 345 BSC, and no threats of war occurred for an entire generation after this date. Such was her legacy that a holiday was created in her honor, one that was held in high regard by the Air Nomads.
Appearances during Aang's life
Aang first saw Yangchen in in a spiritual vision directed by Avatar Roku, where she was seen generating a strong gust of wind in a large field outside a forest.
Later, Yangchen revealed her name to Aang in the Spirit World, at which time the incumbent Avatar was in a coma. During their brief meeting, she was informed of Aang's failure in protecting Ba Sing Se from Azula. Amid the young Avatar's embarrassment, Yangchen convinced him to not feel guilty for his shortcoming, as previous Avatars had also made mistakes and struggled to successfully perform their duties. Although she told Aang very little about her personal experiences, she was very empathetic toward his shame and sadness.
Yangchen also imparted to Aang the reason why the Avatar is incarnated in human form: in order to have a desire in protecting humanity, the Avatar must feel compassionate toward humans, and the only way of doing so was living among them. If the Avatar was instead an all-powerful immortal spirit living at the top of a mountain, he or she would not have anything in common with ordinary people. She acknowledged that the Avatar must experience human life and emotions, such as sadness, anger, joy, and happiness, in order to learn how precious human life is and therefore understand the need to protect it. Thus, with every incarnation, the spirit of the Avatar comes closer to fully comprehending what it truly means to be human.
At the end of the meeting, Yangchen notified Aang that the spirit of the Avatar had been healed, though his ability to use the Avatar State was disrupted and he would therefore need to rely on his friends, not past lives, for guidance. As Aang departed, Yangchen told the young Avatar that the memory of his journey in the Spirit World would be erased once he awoke from his coma.
When on the lion turtle, Yangchen was the last Avatar Aang summoned for advice on how to defeat Ozai without killing him, thinking a fellow Air Nomad would easily sympathize with his views and support a bloodless victory over the Fire Lord. Although Yangchen remarked the Air Nomad belief that all life was sacred, she reminded Aang that the Avatar should disregard such teachings as they stand in the way of successfully accomplishing the task at hand, which was to defeat Ozai. She told Aang to go against his pacifist beliefs and kill the Fire Lord, which deeply discouraged the young Avatar.
Yangchen later led Aang to discover a jointly owned Fire Nation and Earth Kingdom refinery working on sacred Air Nomad grounds.
Appearances during Korra's life
Yangchen was among all the other Avatars when Aang passed on the knowledge of energybending to Korra and restored her bending, representing the newly established connection she made to her spiritual self.
While Unalaq was attacking Raava, Korra envisioned Yangchen among the Avatar lineup she had seen prior to regaining her bending; however, her connection to Korra was severed due to Unalaq's assault on and subsequent destruction of the Light Spirit.
Yangchen, although raised by the Air Nomads, put peace aside to fulfill her duties as Avatar. Although the Air Nomads teachings are to separate one from the rest of the world, she believed that the Avatar can never separate itself from the world because their duty is to it.
When abruptly asked for the name of the female airbender Avatar at the Pacific Media Expo, Bryan Konietzko jokingly dubbed her "Avatar Susan", indicating that they initially did not plan on developing the previous Avatars aside from the two already introduced.