Agnes Nutter

Possibly the greatest fortune-teller and witch ever... shame she's fictional. Stars posthumously in Terry Pratchett's Good Omens as the author of "The Nice and Accurate Prophecies of Agnes Nutter, Witch", which accurately (but not very nicely) predict the future, particularly the Apocalypse. Including the rains of fish.

It's worth mentioning that Neil Gaiman also created Agnes Nutter.

Her last name alone makes for some very amusing jokes--at least if you account for the differences between British and American use of the English language.

For the British, nutter actually means something.

The description of her death in the book is quite 'fun'. Terry Pratchett apparently thought of it some time before for the discworld. However he couldn't use it because he didn't want to kill off Granny Weatherwax (think what she might have done to him if he had tried).

Safety Tip
If you are going to burn someone at the stake - first ensure that they have not filled their pockets with gunpowder and nails.