Orthos

Orthos was the true king of Filtwood Kingdom. He was a Daemon who was thought to be sealed away by a champion named Orthos, but that story was either entirely fabricated, or the daemon managed to kill, and later impersonate the champion.

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, allowing him to evolve from a Greater Daemon to an Arch Daemon.

Story
One day, he tried to trick and kill adventurers, including Shizue Izawa, in order to gain more power, but instead got his Soul devoured by Primordial Noir, killing him completely with no chance of resurrection.

It is revealed by Noir that Orthos is part of the Daemon color line of Demon Lord Guy Crimson.