Maestro (マエストロ Maesutoro) is a mamodo that was one of the 100 trying to become king and was the King of the In-Between World. His power is magnetism. Maestro has no partner due to the properties of the In-Between World. He also appears in the video game Konjiki no Gash Bell!! Yūjō Tag Battle 2 (the Japanese version of Zatch Bell! Mamodo Battles) as a secret boss character.
Maestro was sent to the In-Between World by accident instead of being sent to the Human World and was lost. Eventually, Maestro discovered the kingdom and all the mamodo sent to the In-Between World and became their king. Ever since Maestro bared a hatred against the Mamodo World and all the 99 other mamodo fighting for kingship and vowed revenge. This almost came to be when Maestro summoned Brago, Sherry, Kiyo, Zatch, and Ponygon to the In-Between World to use their power to open the gate to the Mamodo World. Ponygon was not of any use in the In-Between World because Kafk Sunbeam was not there, Ponygon did not have his book, and he cannot pronounce his spells because the only thing he can say is "Meru Meru Me!" Maestro first summoned Brago to the castle and informed him that in the In-Between World he didn't need Sherry to fight and deceived him into believing that burning Zatch's book would open the door to the Human World. After Zatch and Brago's strongest spells collide, the mamodo world door opens and Maestro attacks both mamodo. The fight is one sided with Maestro dominating until Sherry comes at full strength and Brago and Zatch combine their stongest spells to win and burn Maestro's book. Upon going back to the very world he vowed to destroy, Maestro says he's grown to respect his opponents and fades away.