Wherever people are obtuse and absurd ... and wherever they have, by even the most generous standards, the attention span of a small chicken in a hurricane and the investigative ability of a one-legged cockroach ... and wherever people are inanely credulous, pathetically attached to the certainties of the nursery and, in general, have as much grasp of the realities of the physical universe as an oyster has of mountaineering ... yes, Twyla: there is a Hogfather. - Susan Sto Helit.
Susan Sto Helit is a Discworld character. She is the Duchess of Sto Helit and is the daughter of Mort and Ysabell. Or to put that another way, she is the daughter of Death's former apprentice and Death's adopted daughter. Despite having been raised as far away from the occult as possible, taught logic and mathematics and told that fairytales were lies, and even (the coup de grace) named Susan, the most sensible, responsible and un-occult name known in the entire Multiverse, Susan has a few little abilities inherited from dear old Grandfather (not Grandad. Never Grandad).
She can, for instance, walk through walls, TALK LIKE THIS, see anthropomorphic personifications, stop time, and when Death gets sidetracked (which he inevitably does), she has to do the Duty.
Some genetics, as Terry Pratchett notes, are passed on through the soul.
Susan was educated at the Quirm College for Young Ladies (the same place that produced the witch Perspicacia Tick), and has been a governess and a school teacher in between collecting the souls of the deceased, saving young musicians from being killed by the Beat (and the clientele of the Mended Drum), saving the Hogfather from oblivion, preventing the shattering of the Universe, and generally doing what she can to reduce the amount of wantom stupidity in the universe.
In badfic Susan is usually an evil bitch. Pterry refers to her as 'steely', but badficcers tend to make her out as an evil know-it-all, or turn her into an Uber-Feminist!Sue.