Gytha Ogg is a witch in the kingdom of Lancre in Terry Pratchett's Discworld novels. In the traditional triumvirate of witches -- the maiden, the mother and the 'other one', she fulfills the mother aspect, in all the witch novels apart from Carpe Jugulum (where she is forced by circumstances to assume the aspect of 'the other one'.)
Earthy, and a wanton in her youth, she is the matriarch of a huge clan, which pretty much runs the economy of the kingdom. (Her eldest son Jason is a blacksmith that can shoe anything, and her youngest, Shawn, fulfils most of the functions of the royal household from standing army to privy cleaner.) She is an object of terror to her daughters-in-law, and no Ogg would dream of travelling 10 miles from home without bringing her back a present.
Nanny is the author of a celebrated cookbook, The Joye of Snackes in which all the recipes have some relationship to 'funny business' (well, all except "Maids of Honour" -- and even they end up as tarts). She is the object of the dwarf Casanunda's lust, and the owner of a cat Greebo which is one of the most feared creatures on the Discworld in feline form, and on the occasions when he assumes human form (which he's been inclined to do as a last resort ever since the witches transformed him on one occasion) is sexual harrassment on legs -- to Nanny however, he's 'an old softy'.
Nanny is also famed for her singing -- not that it's good, it's just famous -- both for the content, which tends to be bawdy material such as "A wizard's staff has a knob on the end" and "The hedgehog can never be buggered at all"; and for its uncanny ability when combined with the acoustic properties of a tin bath full of water, to terrify the wits out of domesticated animals. When Nanny gets out the bath, the villagers bring in the goats.
She has a face like a wrinkled apple, wears red boots with her witches black, likes a drink, and is a very good witch.