Because the game has so little lore, I took things into my own hands and made him the Frigid Cliff area's former Monster King but he got overthrown by the human kid Ethan(4th boss).

He was then forced to almost constantly push a big crank for a giant wheat grinder to feed the monster armies that were trying to fight against Ellie in-game.
Though I decided he got freed afterward, then another human girl came along and she helped free him by crawled into a small space, then ran off to tell the friendly monsters where she found him; and they teamed up and set off across the worlds to help fix the broken remains of their former lives.