If, as the Discworld version of the popular ' Big Bang theory' states, Great A'Tuin is moving from the Birthplace to the Time of Mating, then at the point of mating the civilizations of the Disc might be crushed, simply slide off, or else the entire world will end. The sex of the World Turtle is pivotal in proving or disproving a number of conflicting theories about the destination of Great A'Tuin's journey through the cosmos. Great A'Tuin's sex is unknown to the inhabitants of Discworld (though in The Colour of Magic Pratchett describes the turtle as male), but the subject of much speculation by some of the Disc's finest scientific minds. The narration has described A'Tuin as 'the only turtle ever to feature on the Hertzsprung–Russell diagram'. Great A'Tuin is the Giant Star Turtle (of the fictional species Chelys galactica) who travels through the Discworld universe's space, carrying four giant elephants (named Berilia, Tubul, Great T'Phon, and Jerakeen) who in turn carry the Discworld.

Pratchett first explored the idea of a disc-shaped world in the novel Strata (1981). The Disc has been shown to be heavily influenced by magic and, while Pratchett gave it certain similarities to planet Earth, he also created his own system of physics for it. It consists of a large disc (complete with edge-of-the-world drop-off and consequent waterfall) resting on the backs of four huge elephants which are in turn standing on the back of an enormous turtle, named Great A'Tuin (similar to Chukwa or Akupara from Hindu mythology) as it slowly swims through space.

The Discworld is the fictional setting for all of Terry Pratchett's Discworld fantasy novels.

The Colour of Magic (24 November 1983 ( )) The Discworld as it appears in the SkyOne adaptation of The Colour of Magic

John keel discworld