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)
Magic is the principal force on the Discworld, and operates in a similar vein to real-world elemental forces such as gravity and electromagnetism. The Disc's "standing magical field" is essentially the local breakdown of reality which allows a flat planet on the back of a turtle to even exist. The force called "magic" is really just a function of the relative absence of reality in the local area, much in the same way that the absence of heat is described as "coldness". Magic warps reality in much the same way as the real universe's gravity warps its space-time. The act of performing magic is, essentially, telling the universe what you want it to be like, in terms it can't ignore. This is very draining to magic users, due to Discworld science's Law of Conservation of Reality (which states it takes the same effort to do something with magic as it would to do it mundanely). This is why most Discworld wizards store magic in a staff (with a knob on the end) which is a sort of capacitor for magical energy.