Ling Yao

Ling Yao is a Xingese character exclusive to the manga and the 2009 anime series. Due to his father, the Emperor's, declining health, Ling left his country to find the Philosopher's Stone to stabilize Xing, as well as grant him the key to immortality. Although he is the 12th son of the Emperor, Ling hopes the Philosopher's Stone will help him rise in the order of succession and achieve the throne thereby securing his clan's welfare. Though he is often laid back and hungry, he's very noble and will do whatever it takes to help his clan. He is also a skilled fighter and has had many incidents involving assassination attempts at his life. He has formed a strong rivalry with Ed, by doing things such as use Ed's money to annoy him. After the 1st Greed is punished by Father, he gives Ling the secret to immortality by transforming him into the succeeding Greed. Ed tries to help, but Ling denies his help as it is the only way to help his clan in the land of Xing. Even while his body is taken over by Greed his mind and soul are kept intact and can come to the surface. Since Greed understands his strong points their relationship is on some kind of symbiotic level. (Source: Fullmetal Alchemist wiki)