Death
Death is a character in the Discworld books. He is one of many anthropomorphic personifications who take on a real existence in the magical field of the Discworld, though it's implied that there may be other Deaths for other worlds. He appears in nearly every Discworld book, and is a central figure (if not always the main protagonist) in his own sub-series of books, most of which also feature his family.
Books
The Death sub-series comprises five novels and one short story:
Death also makes at least a cameo appearance in every Discworld novel except The Wee Free Men and Snuff, with particularly significant appearances in The Light Fantastic, Sourcery and Wyrd Sisters.
The Discworld Death is not the Biblical Death that appears in Good Omens, though the two have many similarities. Another oddly similar character is the Ferryman in Wintersmith. Death is a servant of Azrael, the "Death of Universes" - the other Deaths may be too. (See Reaper Man.)
Adaptations
Death has featured in nearly every Discworld screen adaptation to date. In the animated versions of Wyrd Sisters and Soul Music, he was voiced by Christopher Lee. For the live-action telemovie Terry Pratchett's Hogfather, Death was voiced by Ian Richardson; Lee reprised the role in Terry Pratchett's The Colour of Magic, as Richardson had passed away. In both those adaptations, he was physically performed by Marnix van den Broeke. In the animated film The Amazing Maurice he is voiced by Peter Serafinowicz, who is also the voice of Death for the new Penguin audiobooks.
A very different version of Death appears in The Watch, notable for being the only character played by an American. This version is more similar to the early Death who appears in The Colour of Magic and The Light Fantastic than later portrayals. He is voiced by Wendell Pierce (best known for The Wire), and physically performed by Craig Macrae (who also performs Detritus).