Gudramoth

Gudramoth is the name commonly ascribed to a pit fiend who served as one of the most important generals on the side of darkness during the conflict which led to the Great Shadow.
He had previously been heard of only from a band of adventurers who defeated him in the year EC 4153, sending him back to the Nine Hells. According to them, he had been on the cusp of sinking an entire island, Alekemo of the Lekelic Islands, into the sea after corrupting the vast majority of its population, a campaign which had taken many years. Many scholars theorized that in the wake of this defeat, Asmodeus, supreme ruler of all devils, stripped Gudramoth of some of his powers, explaining his long silence afterwards.
Some ancient texts, primarily The Chronicles of Darkness and Treatise on the War of Shadow, refer to a legion of warlocks under his command at the time of the Great Shadow and in the years leading up to it. When he became inactive, some, though not all, lost their power.
It was assumed for a thousand years that Gudramoth still lived in some form, and this was confirmed during the Eventide of EL 1000, when his chiefest warlock, Mavislak the Blood-eyed, took his form during the Battle of Geldereth. It was revealed that Gudramoth had been relegated by Asmodeus to living as a shadow in the mind of the ghost drow Semraphath, before being passed to Mavislak.
It is unknown what became of Gudramoth following the death of Mavislak, but it is likely that he was demoted yet again, and that it will be a very long time before he is again able to exert any influence over events on the material plane.