Xuanyu Mo

Mo Xuanyu 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.

Mo Xuanyu was described as a lunatic by everyone who knew him, due to a combination of factors including his homosexuality, his interest in demonic cultivation, and the eventual mental break he suffered at the hands of his abusive family following his expulsion from the Lanling Jin Sect.

(Source: Mo Dao Zu Shi Wiki)