Death (Discworld)
Death has appeared in every Discworld novel, with the exception of "The Wee Free Men" and "Snuff", and had a possible cameo at the end of "Johnny and the Dead" (the character was not identified, but spoke in unquoted small caps). The Discworld books with Death as a leading character, starting with "Mort" in 1987, are:
Discworld (world)
Great A'Tuin's gender 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 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. 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 hypothesis is that all stars in the sky are obviously also worlds carried by giant turtles, and that when all the turtles meet they will mate passionately, for the first and only time; from that mating, it is hypothesized that new turtles would be born to carry a new pattern of worlds. Attempts by telepaths to learn more about Great A'Tuin's intents have not met with much success, mainly because they did not realise that its brain functions are on such a slow timescale. All they've been able to discern is that the Great A'Tuin is looking forward to something.