Agahnim
From Zelda Legends Wiki
A wizard who stopped sudden disasters in Hyrule, and was made royal advisor. Actually a pawn of Ganon. Used his power to take over the throne and kidnap the seven sages' descendants. Used their power to break the seven sages' seal. Can only be defeated by bouncing his magic back at him. Also mini-boss of level 4, Dancing Dragon Dungeon, in OoS.