13 Yule Lads live in Iceland, the sons of the old trolls Grıla and Leppalúği. Grıla and Leppalúği keep a pet, a wicked cat, which may sometimes catch children. Grıla, who is big and formidable, was said to collect the naughty children in a sack and take them home to eat for Christmas dinner. If a child is naughty, Grıla finds out immediately. Grıla can't lay her hands on good children.
An old tradition in Iceland is, that 13 days prior to Christmas the Yule Lads start coming down from the mountains one at a time each night. Children in Iceland place their best shoe on their windowsill before going to bed and each night a little gift is left in the shoe from the Yule lad that came down from the mountains that night. If the child has been misbehaving, there might be a raw potato left instead.
The Yule Lads arent as mean as their parents but they aren´t very well-mannered either. The Icelandic Christmas season begins on December 12th, when Stekkjastaur (Sheep-Cote Clod) descends from the mountains. The last one, Kertasníkir (Candle-Stealer) arrives on the 24th of December. Then they leave again to the mountains, one by one in the same order until the last one, Kertasníkir leaves on the last day of Christmas, January 6th.