St. Thorlák's Day, 23 December, is the day of Meat Hook's arrival.

Meat Hook or Ketkrókur, was crazy about meat. In the old days he would lower a long stick through the chimney and snag a smoked leg of lamb hanging from the rafters, or a piece of smoked lamb from the pot. In those days the smoked lamb, which is traditional Icelandic Christmas fare, was cooked on St. Thorlák's Day.

Meat Hook, the twelfth one,
his talent would display
as soon as he arrived
on Saint Thorlak's Day
He snagged himself a morsel
of meet of any sort,
although his hook at times was
a tiny bit short.

Who are the 13 Yule lads and their parents?

The Yule Lads gnomes originated from Icelandic folklore and were portrayed as mischievous trolls that steal food and livestock and scare the children in Iceland.
Care to know more about the other Christmas lads?

Buy set of all the Yule Lads Christmas decorations?

You can get Christmas figurines with the 13 Icelandic Yule Lads here to decorate your home.
Here is a set of all 16 yule figurines
Here is a set of all 14 yule ornaments
Here is a set of all 7 yule lads ornaments