Osiris

 is the King of the Sphinx. Although he had been deified as the Sun God in the ancient age, he's now nothing but a powerful boss of monsters.

Ragnarok Online II
was the leader of the Solvive Empire, which was the most prosperous nation before Morocc. He led the empire with great charisma and presence, but was killed after being poisoned by his brother Set, who was envious of his brother’s success. Following this, Set took over the Solvive Empire. Where Osiris was known as The Great King, Set earned the moniker King of Blood for killing any of the Solvive people who opposed him.

Valkyrie Himmelmez, one of the twelve Valkyries of Freyja, resurrected Osiris using her immense power. However, the resurrected Osiris was not the great King from before but a commander of demons, obsessed with sending heroes to their death using the Blade of Despair. When the Goddess Freyja was locked away Osiris, too, was locked away into eternal darkness.

Trivia

 * Osiris is the name of the Egyptian god of the underworld.