Satan (Final Fantasy II)

Satan is an unseen character from Final Fantasy II. While his existence is only barely assumed in the game, he is directly referred to in the novelization Final Fantasy II Muma no Meikyū.

Story
Satan is the Lord of Pandaemonium at the beginning of the story. His lieutenants include Beelzebub and Astaroth (who is refered to as a male fallen angel, unlike his Final Fantasy IV: The After Years appearance). Emperor Mateus strikes a deal with him to summon hellish creatures into the mortal realm. When the Emperor is defeated by Firion and his friends, the Emperor falls to hell and finally meets Satan in person. Satan is ready to claim the Emperor's soul, but the Emperor resists and defeat him. The Emperor later returns to the mortal realm as the new Lord of Pandemonium.

Etymology
Satan comes from a Hebrew "ha-Satan" which means "the accuser." It is the name of the Devil in Abrahamic religions.