From god to Santa's Helper - What is a nisse?
According to Danmarks Nationalleksikon (Denmark’s National Lexicon), the Nordic nisse originated as a pre-christian house god.
“Legends about the Danish Nisse was first collected and published by J. M. Thiele in Danske Folkesagn (Danish Folktales) (1819-1823). The legends contained older people’s farmer’s tales about the mischievous nisse, who functioned as a protector of the home, as long as he got his porridge the day before a holiday. […] “he is “usually dressed in grey clothing and has in adition a pointy red hat”. He was thus dressed as the farmer […].” [x]
This association with holidays and the appreciation of the folk tales by artists led to the nisse becoming associated with Christmas, especially after the introduction of Santa Claus.
In Denmark today, the nisse is often seen as Santa’s helper, and the mischievous (and occasionally violent) house god became a cute little helper.
(Source)
If you are interested in reading some of these folk tales, I will be translating and posting some from Evald Tang Kristensen's Danske sagn som de har lydt i folkemunde (Danish legends as they have sounded colloquially) (1893) under the tag #talesaboutnisser
