Yule Cat known as Jólakötturinn is an enormous feline monster that roams the countryside in Icelandic tradition during Christmas time.
Size of this creature ranges from being larger than a human to towering over houses and trees, and it's eyes glow in the darkness with an inner light. Otherwise it resembles a normal cat, although in some artistic depictions you can see Yule Cat with small horns.
With it's powerful claws and sharp teeth it can easily chop human adults into bite sized chunks. Little children it was able to swallow whole.
Yule Cat is active during Christmas time, when it may even travel to towns and cities. After Christmas eve it peeks inside windows to see if children have earned new clothes as presents. This seems to act as some form of limitation. If a person had been hardworking and active enough to receive new clothes, they would be safe from Yule Cat's hunger. Had they been lazy, the cat was free to first eat their Christmas meal and afterwards the person themself.
Legend of Jólakötturinn likely dates to somewhere around 1000-1500AD, but in written form the Yule Cat was first sighted during 17th century.
Eventually Jólakötturinn was associated with other Icelandic festive myths. It became the household pet of trolls or giants called Gryla and Leppaluthi, who were also into eating the tender flesh of little children.
Jólakötturinn was probably a story that farm owners used to scare their workers to process wool before Christmas. As time passed, Yule Cat was more readily used to compel good behavior in children. Moreover, the legend also encouraged generosity. Those who were more fortunate with material wealth had a good reason to gift the poor with new clothes during Christmas, as their lives might be in danger without proper apparel.