Quoting from pantheon.org

A tomte (tomten) usually lives at farms in Sweden. If he is treated with respect he can be very helpful. Tomten is very proud and sensitive. If you make fun of him or in any other way treat him disrespectfully, he will most certainly punish you. An "accident" can happen to you, the cows will give sour milk or the harvest will fail.

In fairly modern times people are suposed to give him a white porridge made of rice on a plate outdoors. Closely related to tomten is vätter and huldra, but they usually do not live that close to humans.

It is also the Swedish word for Santa-Claus.

A friend of mine, learning swedish and visiting sweden quite often, started calling me tomte way back ... hmmm I can't remeber, maybe 1989/90...the name somehow got stuck in my brain and I use it as monicker whereever the 'net wants a name from me...Where the name is taken, I change the spelling one way or another (tomten, tomteX, [tomte],...).

As a matter of fact, I can be very helpful if treated respectfuly, but I'm not that particular interested in eating rice outdoors :-)