To find the secret of immortality and become Xingese Emperor
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.
(Source: Fullmetal Alchemist wiki)
