Mumbo Jumbo (sometimes referred to as just Mumbo) is a shaman who helps out Banjo and Kazooie during their many quests. He often transforms either Banjo or Kazooie to fit the situation and help progress further in the game. Mumbo Jumbo has so far appeared in every Banjo-Kazooie game to date.
long before Mumbo met Banjo and Kazooie, he used to be Gruntilda's teacher in magic (there is even a rumor that the two of them dated during that time) until one day Gruntilda used his own magic against him and she turned his face into skull like mask and it will remain that way until the witch has been defeated once and for all. Mumbo still hold hope that she will be defeated and he will get his old face back.