Deumion is a non-playable character in the 20th Anniversary edition of Final Fantasy II. He is an amazingly powerful wizard with the ability to summon holy creatures, and was chosen to be the guardian of the ultimate magic, Destroy. His status as guardian keeps him eternally young.
He appears in the Arcane Labyrinth sidequest as the guardian of the Arcane Sanctuary. He will give the party their ultimate weapons after Phrekyos is defeated. He will reward the party with the Revive spell if he is given the Light of Hope after prompting him with the Hope, or relinquishing Destroy if the party wishes for destruction. His story is told in four related levels of the Arcane Labyrinth stemming from the Jade Passage keyword: Oblivion, Hope, Destruction, and Guardian. His story is implied to have taken place far before the actual events of the game.