A recent Avatar: The Last Airbender fan theory from Reddit contends that the Avatar might not only inherit powers from their own past lives but also from their friends in those lifetimes as well.
The argument is mainly based on a quote from Book 1, Episode 16 in which Avatar Roku says, “I have mastered the elements a thousand times in a thousand lifetimes.” During the first run of Last Airbender in 2005, this was taken to mean that the Avatar cycle had been going for roughly that long. However, in The Legend of Korra it is revealed that the Avatar cycle has only been in place for about 10,000 years since the first Avatar, Wan, fused with the spirit, Rava.
Clearly, this amount of time does not allow for 1,000 lifetimes. So, the fan theory posits that the friends of those Avatars are included in that number of lifetimes and that they inherit power from them as well. While some of the points made seem questionable and flimsy, there are others that seem quite compelling.
The elemental strengths and weaknesses of Kyoshi and Roku are both juxtaposed with their close friendships. Kyoshi is said to have learned all the elements quickly because her predecessor, Kuruk, traveled and was very close with a powerful earthbender, firebender and airbender, but no waterbender. Kyoshi said that water is the element she is the least comfortable with in the second Kyoshi book. Roku, the theory points out, is a gifted firebender like Rangi, and learns airbending very quickly since Kyoshi was close with airbenders. The element Roku struggles with is water and Kyoshi did not travel for very long with any waterbenders.
The most compelling point made by this theory, however, is drawn from an analysis of Avatar Korra’s bending proficiency. Because Aang’s friends, Katara, Toph and Zuko, were all exceedingly powerful benders and represented all three of the other elements, Korra is said to have been a prodigy for the same three elements for that reason. Not only were they powerful, but all of them one-of-a-kind cases. In her old age, Katara is called the best healer in the world in Korra. Zuko was the Firelord, and Toph was the very inventor of metalbending.
The argument goes on to point out that Korra also picked up metalbending in less than a day because of her past life’s relationship with Toph. Conversely, she never learned lightningbending because Zuko wasn't able to either. She could have learned this skill from Mako, a proficient lightningbender, but she’s never shown to possess that ability. The only element Korra struggles with is airbending. The theory contends that this is due to the general lack of airbenders during Aang's life. The series, however, discusses Korra’s difficulty with airbending to be symptomatic of her unbalanced emphasis on the physical nature of the Avatar and subsequent neglect of the spiritual element. Korra even airbends in the Book 1 finale after Amon has blocked her connection to the other elements using his bloodbending.
While the mainstream interpretation of Roku’s statement is merely figurative (1,000 lifetimes just meaning a lot of them), the points in this fan theory cannot be easily dismissed. Though missing from the original Reddit post, in Book 2, Episode 1, Roku also tells Aang, “The Avatar state is a defense mechanism designed to empower you with the skills and knowledge of all the past Avatars.” The skills and knowledge could easily include those of the past Avatar’s closest friends.
While there are some holes in the theory, overall, this is a very plausible hypothesis for the bending traits demonstrated in the Avatar cycle.