Acererak

Acererak was a lich who constructed the Tomb of Annihilation and the infamous Tomb of Horrors.

Description
An exceptionally powerful lich who often wielded powerful artifacts, such as a Talisman of the Sphere, Acererak spent his days scouring the multiverse for more of such artifacts, which he hid in the legendary, trap-filled tombs he constructed, hoping to lure in adventurers and treasure hunters, whose souls were fed to his phylactery, stored on a hidden demiplane, when they inevitably fell to the dungeon's defenses. After his failed attempt at ascending to godhood, Acererak lost interest in being worshiped, instead inflicting great suffering upon those few followers he did have.

History
Much of Acererak's History was forgotten, but it was believed that he built the Tomb of Horrors during the Age of Empires. After centuries of resting within the tomb, Acererak accepted his transformation into a Demilich, choosing to roam the planes as a disembodied consciousness, inserting Soul Gems into his skull's eye sockets, in order to absorb the souls of any who dared to disturb his rest. During this time of contemplation, Acererak discovered many of the secrets of the Negative Plane including the existence of Atropus and, upon being awakened by unfortunate adventurers whose souls were consumed in the tomb, hatched a plan to absorb the power of the Negative plane, effectively becoming a deity of raw Negative Energy and gaining the ability to possess the body of any undead in existence. Although it came perilously close to success, this plot was foiled by adventurers delving into the Tomb of Horrors (and the city of Moil beyond) in the year 489. After this defeat, Acererak once again fell into obscurity, although his memoirs were recovered by one of the heroes who foiled his attempt at apotheosis and eventually fell into the possession of Lysander Titanblood.

Acererak resurfaced at some point in the 13th century in Azlatlan to construct the Tomb of Annihilation.