His name–or Her name, according to another school of thought–was Great A'tuin; he–or, as it might be, she–will not take a central role in what follows but it is vital to an understanding of the Disc that he–or she–is there, down below the mines and sea ooze and fake fossil bones put there by a Creator with nothing better to do than upset archaeologists and give them silly ideas.
—  Terry Pratchett, The Light Fantastic

“There was no analogy for the way in which Great A'Tuin the world turtle moved against the galactic night. When you are ten thousand miles long, your shell pocked with meteor craters and frosted with comet ice, there is absolutely nothing you can realistically be like except yourself.

So Great A'Tuin swam slowly through the interstellar deeps like the largest turtle there has ever been, carrying on its carapace the four huge elephants that bore on their backs the vast, glittering waterfall-fringed circle of the Discworld, which exists either because of some impossible blip on the curve of probability or because the gods enjoy a joke as much as anyone.”

—  Sourcery- Terry Pratchett