There´s someone in the walls of Scandinavians
Domestic spirits are quite common across cultures, so it´s not surprising that there are such creatures in the Scandinavian folk tradition.
The names differ in different parts of the region, but essentially it's the same character. Tomten derives from ‘tomt’ - Swedish for ‘site, house’, so Tomten is literally ‘the house creature’. Nisse is a little more complicated. The most plausible version is that it comes from St. Nikolas (Nisse can be a short form of Nils/Nikolas), as these spirits are associated with Christmas which happens shortly after St. Nikolas´s day. Then there’s a version saying it comes from Nixie - Old Norse water monster, which doesn't fit the house spirit in question.
It's a small human-like creature in a red hat and grayish clothes, usually with a white beard. They live in a barn or in a basement, sometimes in a tree near a house, but it depends. It is believed that Tomten/Nisse brings prosperity to hard-working people and helps them around the house, but punishes negligent housekeepers by injuring their stock, messing with the harvest and sometimes even setting the house on fire.
The hat is red for a reason, actually. In Indo-European cultures red hats are associated with evil spirits (think about Red Riding Hood, the story can be interpreted either as about losing virginity or sending the spirit of an already dead Grandma to the Other World - for this I'm relying on Alexandra Barkova).
One other interesting detail - Tomte/Nisse is good at playing the violin and can teach you to play in return for a gray sheep.
Illustrations are by Jenny Eugenia Nyström
Special thanks to komixo!