The troll is a mythical creature of Scandinavian origin that has become a popular staple in the realms of legend, folklore, and fantasy. One of the most anthropomorphic fantasy creatures, trolls have been depicted in vastly different ways. From their Scandinavian fairy tale roots, in such tales as Three Billy Goats Gruff, trolls have achieved international recognition, and in modern fantasy literature and role-playing games, trolls are featured to the extent of being stock characters. Generally considered somewhat dangerous, whether through their larger than human size and strength or through more magical means, trolls are recognizably similar to human beings. A school of thought has it that the mythical trolls originated in knowledge, if not memories, of Neanderthal humans. Whatever their origin, trolls represent that which is somewhat peculiar and different, yet hauntingly similar to ourselves. Efforts to depict trolls in literature, art, music, and other cultural forms, may reflect our desire to embrace, yet at the same time fearing, those who are different.
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In the first tradition, the troll is large, brutish and a direct descendant from the Norse jötnar. They are often described as ugly or having beastly features like tusks or cyclopic eyes. This is the tradition which has come to dominate fairy tales and legends, but it is also the prominent concept of troll in Norway.
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The second tradition is most prominent in southern Scandinavia. They are usually small, mysterious creatures that live in dark dwellings and are mischievous. Often than not, the trolls kept themselves invisible, and then they could travel on the winds, such as the wind-troll Ysätters-Kajsa, or sneak into human homes. Whereas the large, ogre-like trolls often appear as a solitary being, the "small" trolls were thought to be social beings who lived together, much like humans except out in the forest. They kept animals, cooked and baked, were excellent at crafts, and held great feasts.

Like many other species in Scandinavian folklore, these trolls were said to reside in underground complexes, accessible from underneath large boulders in the forests or in the mountains. These boulders could be raised upon pillars of gold. In their living quarters, they hoarded gold and treasures. Opinion varied as to whether or not the trolls were thoroughly bad, but often they treated people as they were treated. Trolls could cause great harm if vindictive or playful, though, and regardless of other things they were always heathen. Trolls were also great thieves, and liked to steal from the food that the farmers had stored. They could enter the homes invisibly during feasts and eat from the plates so that there was not enough food, or spoil the making of beer and bread so that it failed or did not become plentiful enough.
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www.newworldencyclopedia.org/entry/Troll