Kwartz

Troll mentioned in The Light Fantastic, his name is a homophone of quartz. Kwartz is an example of how trolls, dull and slow-witted in the heat of the city, are bright, rational creatures when in their preferred environment. He and his extended family offer assistance to Rincewind in such matters as finding onions, avoiding Herrena the Henna-Haired Harridan and her mercenaries, and the vital necessity of not lighting a fire on Old Grandad's tongue.