Dennis's Granny, voiced by Sally Grace. Although she is eighty years old, Dennis's Granny is still very young at heart. Dennis loves his Granny, he defends her when another speaks ill of her ("Dennis and the Beanstalk"), and will come to her for advice in times of need ("The Day TV was Banned").
In her youth, Dennis's Granny was every bit the Menace towards anything like a peaceful society in Beanotown that her grandson is today, as revealed in "The Secret Diary", and in her day there was a police officer, Sgt. Boot, who was the "Sgt. Slipper" to her "Dennis".
According to information from the Beano comic, she is the mother of Dennis's Dad; in "The Secret Diary", when Dennis's Dad mentions more than once how well-behaved he was to his parents, he may have been referring particularly to his father because Dennis's Granny favours her grandson, Dennis, who takes after her.
In "The Secret Diary", she was depicted as having black hair, like her son and grandson, but in "Gorilla Warfare", she was seen in a flashback with blond hair (so possibly she dyed it). She rides a motorcycle and eats pizza with "everything on them". She is perhaps the only adult, as mentioned by Dennis's Dad, "insane enough" to provide Dennis with any adult supervision and survive intact; she will even willingly come back for more of the fun and mayhem.