Morimbuul is the daemon tutor of the Blood Congregation. He entered the Prime Material Plane in the year 318 AF through a rift in his own plane. Due to the interference of a priest named Valeo and his angel, the rift was sealed before any more of Morimbuul's demonic brethren could pass through. Xerimor, who had opened the rift, bound Morimbuul into slavery and forced him to teach all he knew of the daemonic arts. This led to the founding of the Apostate's guild which is now known as the Blood Congregation.
Over the years, Morimbuul has revealed himself to be a deceptive creature; he constantly schemes to escape his confines, and has on more than one occasion summoned red daemons to hassle the citizens of Mhaldor. He raped three highly-ranked Mhaldorian women - Tyn, Ladydeath and Ravai - and through them, respectively, had three half-demon offspring: Sabatu, Nebatu and Aznahz the Haruspex.