Spoiler

One of the original people, and the creator of the Houshin plan. He has the peopei Dashinben, Taikyokuzu, Chusenjin (snow that damages the soul), and Bansenjin. Fearing Jouka's revival, he chose to remain and not merge with the earth like the other original people. He became a human named Ou Eki and approached the Sandai Sennin with the Houshin plan, becoming Genshitenson's disciple. Genshitenson, realizing Ou Eki's ability to split his soul, divided him into two, returning one to Ou Eki (who would be traded with Tsuten Kyoshu for Youzen, and would become Otenkun) and keeping the other, eventually placing it in Ryou Bou, a deceased baby of the Kyou tribe (who would become Taikoubou). Ou Eki loses his memories of being one of the original people, and does not regain them until Taikoubou and Ou Tenkun merge to create Fukki. After merging, Fukki retains the ability to split, and can return to being Taikoubou and Ou Tenkun at will.

(Source : Wikipedia, edited)