Spirit guide
The essential partner for any spiritualist or medium. The person who picks up the phone when the medium dials the next world. Traditionally, the role calls for a North American Indian or nearest equivalent, who have something of a cachet in spiritualist circles.
On Discworld, Mrs. Evadne Cake has the services of One-Man-Bucket. (Reaper Man)
On Planet Earth, Madame Tracy calls upon the services of Geronimo. Tracy has read somewhere that Red Indians encapsulate the wisdom of generations, passed down from shaman to shaman, and among their number can be found some of the most spiritually pure, wise and compassionate discarnate entities who are, for instance, happy to assure mrs. Doris Williams that mr. Fred Williams (deceased) is here among us and is happy with his life in Spirit, and that death is but a sleep.
Newton Pulsifer has also read about the Apache chief Geronimo, and doesn't have the heart to tell Tracy that in life, Geronimo was a member of a tribe whose word for "person not an Apache" was cognate with "To be hung by the ankles with their head inches away from a roaring fire, until their skulls explode". In other words, just as Skund has the other sort of Elves to the wise and nature-loving beings envisioned by Twoflower, this is the other sort of Indian: a murdering sadist with a yen for inventive and agonising torture.