Beherith

In the Eye of Anubis, Beherith was the Vestige of an fiendish being of such terrifying power that even in its reduced circumstances, it was still capable of commanding the loyalty of archfiends.

Faustian Vestige

In return for human sacrifices of people from bloodlines significant to religions, Beherith would allow a Binder to contract with it and grant them immense power, as well as access to its infernal servants.

Anuberith & the Jackal Wars

One contractor, a human acolyte of the faith of Anubis named Menetnashte, used this power to create a blasphemous hybrid cult (the Cult of 'Anuberith') and conquer a vast empire centered on Prime Material Har'Akir, long before the birth of Ankhtepot. The Cult and the empire eventually fell in spite of the infernal might provided by Beherith; Menetnashte was unable to renew their pact because her intended sacrifice was spirited away by his mother and subsequently deposited in Sri Raji by the intervention of the Dark Powers, while a coalition of allied religions of the gods attacked the empire.

Imprisonment

The collected priests imprisoned Beherith in Menetnashte's heart, extracted it from her body and transformed it into a giant emerald: 'the Eye of Anubis'. Sealing the Eye in a heavily-warded tomb and appointing Menetnashte as its not quite alive, yet undying guardian, the coalition of faiths thought they had defeated the vile Vestige forever.

The Eye in Ravenloft

The coalition had no way of knowing that Ankhtepot's actions would lead to a debased version of Har'Akir becoming part of the Amber Wastes -- or that the Dark Powers would bring the tomb, its prisoner and its guardian along for the ride to the Demiplane of Dread.

With Ankhtepot eager to rid himself of Beherith's presence as soon as he became aware of it, information was leaked to the Fraternity of Shadows which would lead to a running battle between the Menetnashte Expedition and John Lancaster Cavendish over who would be first to claim the gem.

The battle ended in Port-a-Lucine, where the Ash Knight Sascha Dzemianovitch spited Cavendish by contracting with Beherith by offering the life of a person of religious significance to the Vestige: his own. As the pact was valid and bound man and Vestige together as one, his subsequent death by suicide also spelled Beherith's end. The Vestige seemed to implode upon itself, dragging Cavendish along in its death throes.