So during the wait for the next episode to come out, I thought I'd share my thoughts and theory on who the Second Avatar after Wan was and his life story. I'd love to get some miniseries (hopefully) on this second avatar since 1) he probably witnessed the divergence of the world into four nations, which undoubtedly shaped the plot of the Avatar universe after, 2) he was the first Avatar to be able to communicate with a past life (Wan being the FIRST ever Avatar could not since he was the only one at his time). So here are my thoughts:
Introduction
After Vaatu was defeated and imprisoned in the Tree of Time, the Lion Turtles descended into the Void and let go of their earthly duties of protecting the humans. However war began among the Earthbenders, and Avatar Wan decided to intervene. He was unable to prevent them from war and was mortally wounded in combat. Coupled with old age, his body could support him no more and he died in the battlefield. Soon Raava's spirit descended upon a new Avatar Jiro (二郎, basically Japanese for "next", "second").
Jiro was a male Air Nomad (from the cycle with Roku, a male firebending Avatar, had Aang, a male airbending Avatar, as his successor). He was born in the Air Temple, in the fall of the year after Wan's death. As a child, Jiro had successfully become an airbending master at the age of 16, having successfully invented the glider. The monks of the temple noticed some signs of him being the Avatar possibly, so they picked up Wan's teapot and put in a box of materials and told Jiro to choose one item. And indeed, Jiro chose Wan's teapot. Upon this, the Air Nomads declared to the rest of the world that the new Avatar was found. (The custom of announcing the new Avatar at the age of 16, and the Air Nomads's practice of having a kid pull out a previous Avatar's item, all originated from here.) Jiro travelled the world to learn the remaining three elements and succeeded by the age of 18.
Born as an Air Nomad, Jiro had a pacificist policy. Unlike Wan who responded to conflict with intervention, Jiro responded with a laid-back attitude and let the conflict ease out. However, in communicating with Wan, Jiro learned that the Avatar had to dedicate him or herself to worldly affairs because of the nature of the duty, and that any personal philosophy must be rejected to achieve this.
Establishing the Earth Kingdom
With this in mind, Avatar Jiro set sight upon the Earth Kingdom war that was going on. At the time, the Ba Sing Se warlord had conquered most of the territory in the eastern part of the continent and dominated the war. He eventually grew so powerful that he declared himself the 1st Earth King and threatened to wipe out the entire opposition in the Earth Kingdom. Jiro feared that the aggression of the Earth King would destroy the lives of the Earth Kingdom citizens. He fought against the army of the Earth King himself and eventually forced him to the table to sign an peace plan with the warlords, and the numerous leaders of the Earth villages. After many days of persuasion, they finally struck a deal. The Earth King was to maintain rule, at least in name, over the entire east continent and declare it as territory of the Earth Kingdom. The warlords were to submit to the Earth King's rule but they could have their own army, currency, social order, etc. In the face of threat, however, they were to protect the Earth King's interests. Satisfied, the Earth King returned to Ba Sing Se and did not leave the city to his death. However, it was widely believed that the 1st Earth King did not die a natural death; Jiro double-crossed the ruler by luring him to the Crystal Catacombs and murdering him in there, fearing that the Earth King's intimidating presence would destroy the hard-earned peace and balance in the Earth Kingdom. The Avatar then placed a ruler who was more pacifistic person and named him the 2nd Earth King. What Jiro did not see was that this 2nd Earth King was much weaker than the 1st and was unable to keep hold of the large and diverse Earth Kingdom. As a result, the Earth Kingdom became the loosely organized confederation state it is until today, but Avatar Jiro could do nothing about it.
Meditation to the Spirit World
Avatar Jiro was deeply in shock after he murdered the Earth King, believing it to conflict with his own Air Nomad pacificism. Wan reassured him that he did it for the right cause and that the pros of his action outweighed his cons. Jiro's actions were to be replicated by Avatar Kyoshi thousands of years later. Avatar Jiro then journeyed to the Water Tribes, where he helped usher in harmony and peace by building a grand city in the North Pole to unite the Tribes together. He also took advantage of the great spiritual energy in the North Pole to start meditating there to help solve his mental problems. Through this he became the first Avatar to gain access to the Spirit World through meditation. After his travels in the Spirit World he cleansed his mind and helped himself gain ground.
Organizing the Fire Sages Council
Avatar Jiro journeyed to the Fire Nation (technically just a mass of land) where after many years, the Sun Warriors civilization of Wan's time declined. The Fire Land then lived in a state of no order until Jiro came. Jiro decided to restablish order by hand-picking some of the most skilled and spiritual firebenders and established them as Fire Sages. He then organized a council of these Sages to rule the nation, believing this plan would work better than what he did with the Earth Kingdom. Through these actions Jiro united the Fire Nation and established order again. However one Fire Sage deemed himself to possess the best firebending skills out of all of them and was outraged when Jiro forced him to submit to equal status as firebenders inferior to him. Shortly after Avatar Jiro's death, the Fire Sage quickly accelerated his plans and took power for himself, reforming the country into an empire and declaring himself the 1st Fire Lord, and ended the spiritual reign Avatar Jiro had established.
Return to the Air Temples
After 30 years of travelling the world in hopes of continuing Wan's goal and establishing balance in the world, Jiro returned to the Air Temple. Now, when I say Air Temple I only meant one; in fact the Airbenders simply lived collectively together. Over time, Jiro decided that he became too old to journey the world and constantly maintaining balance among the nations. He called for his fellow Airbenders to be like him and roam around the world. To assist this effort, Jiro built the four Air Temples located in a remote place in each part of the world. In addition, after many years of thought, Avatar Jiro named some of his old friends during his travels. They came from all over the world, were all greatly spiritual, highly skilled in bending, and very knowledgable scholars. They met together in the Misty Palms Oasis and there Avatar Jiro formed the Order of the White Lotus to maintain a measure of connection and balance between the Fire Nations. After this he resided in the Northern Air Temple, feeling that he had established a system of peacekeeping and that he had successfully delivered Wan's goal.
Later years
In some time later in his life, Avatar Jiro met Guru Laghima in the Northern Air Temple. Jiro personally loved the Guru's poetry and sought to meet him for spiritual advice. However, upon meeting the Avatar, Guru Laghima accused Avatar Jiro of disrupting the ways of life among the humans in the world by seperating them into nations. He argued that Avatar Jiro was too bounded by earthly tether and constantly tried to remain active in solving the world problems. Laghima proposed that Avatar Jiro should maintain his spiritual roots in airbending culture and allow the world to progress naturally. Avatar Jiro put up a fierce counterattack to this and the two left each other unhappily.
Laghima's prophecy became true. Shortly after Jiro died at age 70, the Fire Sages as aforementioned divided and the Fire Nation Dynasty was established; and in the Earth Kingdom, the local warlords took advantage of the 2nd Earth King's weak nature and began conflicts to increase their states again, only not as frequent as before in fear of the Avatar's power. However there were still positives as Jiro had established a greater measure of peace and balance than Wan before him, and it was not an exaggeration to say that Jiro was a worthy successor to Avatar Wan.
Basically, what I think was the highlight of Jiro's tenure as the Avatar was:
1) As a plan for peace, Jiro separated the world into the Four Nations, establishing the political map of the world that maintained to this day.
2) Forming the Order of the White Lotus to also keep the Four Nations in check, by calling together a group of highly connected and skilled benders from all over the world.
Now what about the next 3rd Avatar? Hmm...I'm thinking that it would be the first female Avatar. Unlike Jiro, she was fierce and rebellious, especially when the customs of the Water Tribe favored men and she was unable to begin bending training as the Avatar. So she journeyed to the South Pole and split the Water Tribes into two. If you guys want, comment on this thread to continue the story of the next Avatars!
Thanks for reading. :)