Morimbuul was daemon tutor to the House of the Blood Congregation. He entered the Prime Material Plane in the year 318 AF through a rift from his home plane. Due to the interference of a Priest named Valeo and his angel, Sophia, 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 that he knew of the demonic arts. This led to the founding of the Apostate Guild, eventually known as the Blood Congregation.
Over the years, Morimbuul has revealed himself to be a deceptive creature; he constantly schemed 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.
Morimbuul currently serves his penance within Mhaldorus, after being eaten alive by the Daemon Guardian.
Morimbuul's intense desire to free himself is reflected in the deck of legends, in the Morimbuul card.