Orthos

Orthos was the true king of Filtwood Kingdom. He was a nameless demon who was thought to be sealed away by a champion named Orthos.

Background
Orthos was one of the few cases of self-naming. As a man-made hero, the voices of his nation's people gave him power, that power gave him a name allowing him to become a named being on his own.

He later on tried to trick and kill adventurers in order to gain more power, but was defeated by another demon.