I was supposed to post this before Christmas but never got around to it. Most Norwegians, and other Scandinavians, has grown up with this folklore.
The Norwegian Fjosnisse lives on farms and looks after the animals as well as the farmer, the farmer's family and the house, he usually does this at night so that nobody sees him. He is very small, no bigger than a horse's head and by turning his red hat inside out so the grey insides is facing out, he can make himself invisible.
The Fjosnisse is easy to offend and if you do offend him, maybe by not leaving porridge out for him at Christmas, he might retaliate by doing little pranks like tying the cows tails together or something worse like kill them! So it's important to make sure you don't do anything to offend him.
Some ways of offending the Fjosnisse can be; swearing, treating the animals bad and changing the way things are done on the farm (the Fjosnisse is a traditionalist).
The Fjosnisse is not the one that brings gifts at Christmas, that's the Julenisse (Santa). Although there might be a present or two from the Fjosnisse as well, probably the years when he feels particularly happy and appreciated.
We have some years, even though we don't live on a farm any more, left porridge out for the Fjosnisse. You know, there are so many farms that has been shut down that a lot of the Fjosnisser doesn't have a place to live now but they still deserve a Christmas treat.
This is what I've grown up with to know as the Fjosnisse, apparently there are a few different versions of him out there as well. But the main thing in all of them is that he lives on farms and you'd better not piss him off.