Acererak

Acererak is an ancient, undead villain who created the Tomb of the Nine Gods. When Diath asked Shemeshka about the death curse, she told him to learn everything he could about Acererak.

Strix found out where Acererak's Tomb of Annihilation was when she adventured with the Acquisitions, Inc. crew. The oracle at Orolunga told the group that Acererak's phylactery is "not on this world."