Zizmor is the head of the society of wizards. He only appears in two books (Revenge of the Dragon Lady and Danger! Wizard at work!) but Zelnoc mentions him almost every time he appears to Wiglaf and his friends
In Revenge of the Dragon Lady, Wiglaf needs help from Zelnoc so he can be safe from Seetha because Wiglaf slew her favorite son Gorzil. Zelnoc said that he knew a courage spell, but it would frequently screw up. He called Zizmor instead, who gave Wiglaf a triple courage spell which allowed him to defeat Seetha.
In Danger! Wizard at Work! Zelnoc accidentally turns Wiglaf, Angus, and Erica into dragons. Erica called Zizmor to put things right - only to find a baby. Zelnoc also appeared, explaining his"Get Younger Spell" worked too well. He reversed the spell on Zizmor, who turned them back to humans.
Zizmor, like all wizards can be called by saying his name backwards thrice. In this case, it would be Romziz.