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:
Death (Discworld)
Susan Sto Helit is Mort and Ysabell's daughter and only child. When she first appears as a schoolgirl in "Soul Music", Susan has just inherited the duchy on the death of her parents. From the time she was a small child until the start of the book, when she is sixteen, her parents have hidden her background from her and brought her up to be logical, and it comes as a shock when the Death of Rats and Quoth the raven come looking for her. She has to act as a stand-in for Death when he disappears, but subsequently returns to her education. Despite the fact that she has inherited all of her grandfather's abilities, she longs to be normal, and gets human jobs, first as a governess (in "Hogfather"), and then as a schoolteacher (in "Thief of Time"). Death is constantly dragging her back into the world of the occult. At the end of "Thief of Time", she begins a relationship with Lobsang Ludd, the anthropomorphic personification of Time.