Acererak is a powerful demilich who was known and feared by many in the multiverse.He visited Toril in the late 1480s DR to place an artifact created with the help of Dendar called the Soulmonger in the Tomb of the Nine Gods, causing the onset of the Death Curse.
Acererak traveled through the multiverse in search of artifacts, which he liked to lock away in trap-ridden dungeons to watch adventurers suffer and die. He then enjoyed trapping their souls in his phylactery, whose location was unknown.
Although having had the power and opportunities to ascend to godhood, Acererak had no interest in being worshiped, despite having his share of followers whose suffering he enjoyed watching.
Much of Acererak's past history was forgotten. It was believed that he was originally from Oerth.
At some point in the 15th century DR, Acererak went to Chult and defeated the Nine Trickster Gods of Omu. He then enslaved the Omuans and forced them to build the Tomb of the Nine Gods. Acererak killed all the Omuans after the tomb was completed, and buried them alongside their gods.
At some unknown time not long before the late 1480s DR, Acererak traveled to the Astral Plane and found the Atropal who took to calling himself Larry. For reasons not entirely known, he decided to nourish to godhood. For that purpose, he built a powerful artifact called the Soulmonger and placed it in one of the tombs he possessed, the Tomb of the Nine Gods. The tomb served as the atropal's nursery while the artifact nourished it by trapping the souls of the dead and draining the souls of those who had been beneficiaries of Resurrection magic. This was known as the Death Curse