A troll is a supernatural being in Norse mythology and Scandinavian folklore. Troll may have been a negative synonym for a jötunn (plural jötnar), a being in Norse mythology. In Old Norse sources, beings described as trolls dwell in isolated rocks, mountains, or caves, live together in small family units, and are rarely helpful to human beings.
Later, in Scandinavian folklore, trolls became beings in their own right, where they live far from human habitation, are not Christianized, and are considered dangerous to human beings. Depending on the region from which accounts of trolls stem, their appearance varies greatly; trolls may be ugly and slow-witted or look and behave exactly like human beings, with no particularly grotesque characteristic about them. Trolls are sometimes associated with particular landmarks, which at times may be explained as formed from a troll exposed to sunlight.