Yao Fei was formerly a member of the People's Liberation Army, wanting to become a doctor. Unfortunately, he was used as a common soldier and forced to kill the enemies of the state. After refusing to kill any more people, he was labeled a deserter and shot. He escaped and awoke, healed, on the bed of local physician.
The physician was the father of Tenzin Cering, the unarmed man Yao had just killed. Tenzin was next in line to become the Accomplished Perfect Physician, a man with the memories and abilities of all his predecessors. Instead, Yao was chosen to be the seventeenth Perfect Physician. After this, Yao used his powers for good while remaining an renegade and enemy of the state.
However, when he realized that he could do more by joining the Great Ten, he became a member of the team, playing the role of diplomat and trying to keep the team from doing any senseless slaughter.