Mo Xuanyu (莫玄羽, Mò Xuányǔ) was one of Jin Guangshan's illegitimate sons and a former disciple of the Lanling Jin Sect. He sacrificed his soul to summon an evil spirit, Wei Wuxian, to exact revenge on the Mo family on his behalf. In his living days and even during Wei Wuxian's possession of his body, he was described as a lunatic. (Source: Mo Dao Zu Shi Wikia)