Gruntilda, also referred to as Grunty, is a foul-tempered witch and the main antagonist of the series. Her appearance is remarkably similar to the principal antagonist of The Wizard of Oz. She has green skin, warts, a pointed hat and a high-pitched cackle, as well as a penchant for speaking in rhymes. She has three sisters: Brentilda, Mingella and Blobbelda. Brentilda is her complete opposite, with a fairy-like appearance. Mingella and Blobbelda convince Grunty to stop speaking in rhymes, although she resumed the trait in Nuts & Bolts. Gruntilda's surname, Winkybunion, was revealed in the ending cut scene of Banjo-Tooie. She is a skeleton in Banjo-Tooie, she is a robot in Banjo-Kazooie: Grunty's Revenge, and has an artificial body in Banjo-Kazooie: Nuts & Bolts due to Banjo and Kazooie defeating her at the end of the previous games.
Source: Wikipedia, "Banjo-Kazooie (series)", available under the CC-BY-SA License.