The gigantic tortoise upon whose back the Discworld rides, in the popular Terry Pratchett series.

Actually, four elephants stand on the tortoise, and the disc rotates upon their backs. There are no good theories to explain the tremendous friction.

Great A'Tuin is female, and is now a mother.

The wizzard Rincewind once had a very close encounter with the Great A'Tuin (which involved falling off of the Disc).