Ussü was the High Mage and Advisor to Yeull 'ul Taith, the self-styled "Overlord" of Fist. He had been a cadre mage during the Korelri Campaign and stayed loyal to the Malaz 6th Army when it went renegade and cut ties with the Malazan Empire. Because Fist's patron goddess the "Blessed Lady" prevented mages from accessing any Warrens but her own, he pursued his old Mockra-based divinatory powers by other, darker, means, including experimenting with blood sacrifices. His three apprentices, Seel, Temeth, and Yurgen, assisted with his efforts.