A mysterious and powerful villain who is after Sakura's feathers. He is later revealed to be a direct descendant of Clow Reed and well aware of the powers of the Dimension Witch. He was the one who imprisoned the real Syaoran and created the Syaoran who is the protagonist of Tsubasa. Though he already possesses the power to cross dimensions like the High Priest of Clow and Princess Tomoyo, he seeks the power of Sakura's wings, which surpasses the power of all who can cross dimensions, and the power that lies under the ruins of the Clow Country in order to "bring back a dream that has already ended".
This is later revealed to be a euphemism for bringing back the dead. He does not care on how much blood has to be shed to get that power; those he has killed (or arranged to be killed) include Kurogane's mother, Xing Huo and the real Fai. His true objective is not to obtain Sakura's feathers; rather, the scattering Sakura's memories was to provide a motive that would force her to travel between dimensions to recover them and attain the physical memories Sakura gains through her powers as she visits various dimensions. Therefore the scattering of memories and having the TRC trio accompany Sakura on her journey was a pre-planned situation created by Fei Wong in order for him to attain his wish, which apparently is to revive someone from the dead. In Chapter 122 of xxxHoLiC, Yuuko reveals in a monologue that he is responsible for the soul stealing entities featured in Volume 5.