First mentioned in chapter 2082, Unknown King used to be the Guild Leader of Unyielding Soul. Due to his old age and deterioration, he had retired from the frontlines two decades ago.
He is also the grandfather of Mu Lingsha.
He is old but he presumably looks particularly young due to the S-Rank Nutrition Liquid.
Class: Tier 2 Assassin 
Realm of Refinement: Domain Realm
Unknown King is a peak expert from one of the older generations. He used to be Unyielding Soul's Guild Leader and was active when Unyielding Soul was still at its peak. Everyone knew the nickname "Thousand Hands" and he was among the top three assassins in the virtual gaming world. If not for his physical deterioration he would have still been active as Unyielding Soul's peak experts and the guild would not have fallen to its current state.
When Unknown King was first introduced, he had been present with Mu Lingsha in a top-VIP room, discussing Zero Wing's chances on winning the management rights for White River City's First Auction House Competition.