Zofis is a mamodo who helped Koko, Sherry's friend, to get revenge on the city that she suffered in. Zofis also controlled Koko so he can be mamodo king.
Zofis, under the guise of a mamodo called Milordo-Z, attempts to get Zatch and Kiyo to fight his side, as he collected and released the millennium mamodos that were sealed away in stone a thousand years ago to create an army, but he needed someone to help him lead them into battle.
It has been speculated that Zofis is female in the Japanese version, however, creator Makoto Raiku apparently states that Zofis is indeed male.