Jamirus is one of the four Dread Fiends and a major antagonist in Dragon Quest VI. He is a cunning, three-eyed griffin who is adept at giving speeches to his fellow monsters and coming up with schemes to gather victims for sacrifices in the name of the Archfiend.
He devised a plan in which he used his monster minions, who were disguised as humans, and a moving island to lure the people from the town of Aridea to a make-believe land of fantasy and happiness called the Isle o' Smiles; which supposedly appears at night only. As soon as the gullible townspeople reached their destination, which turned out to be really a demonic shrine, they got sacrificed to the dark gods.
After he's defeated by the heroes, the dream selves of all who were sacrificed are set free, which includes King Medford and his palace, who's now avaliable for the Hero to bring in his Mini-Medals. The hero also gets to keep the moving island, which can be used as a boat in the Dream World.
In Dragon Quest Monsters: Joker 2, he is a cohort of Gemon and can be obtained through synthesis of a Pazuzu and a Gryphon.
Dragon Quest I