The jólasveinar, or "yule lads", are a traditional part of an Icelandic Christmas.  The jólasveinar are:

From December 12 until Christmas Eve, the yule lads come down one at a time from the mountains.  Each has a personal trick, such as stealing milk or slamming doors.  They often leave presents for good children, and sometimes a potato for the bad ones.  In olden times, the yule lads - who were themselves the children of monsters - had a much darker nature.  They were so feared that in 1746 a law was passed to prevent them being used to frighten children.