In some of the Lucia manhwa’s translations, his name is written as “Quayz” (iirc).
And yes, i agree with you about not liking him

In Korean historical dramas, i think “hwangbi mama” means “queen dowager” (the former king’s wife & the current king’s mother, wheter it’s biological or step mother).
For the title “mama” only, it could also be used for the king himself