Rat Cook

The rat cook is the subject of legends and myths in the Seven Kingdoms.

According to these legends, a king once paid a visit on the Nightfort, then the chief castle on the Wall. The king insulted the food of the castle's cook. Incensed with rage, the cook killed the king's son and served his flesh in a pie to the unknowing king. The king enjoyed the pie so much he asked for a second helping.

The gods cursed the cook by turning him into a fat, white rat which could only survive by feasting on its young. He was condemned to run the halls of the Nightfort. The gods were not offended by the murder or even the cooking of the prince, but by the cook breaking the laws of hospitality and protection, which are held to be sacred above all others.

In the books
The story is much the same in the books, except for the detail that all of the rats in the Nightfort are its descendants. The king in the story is identified as an Andal ruler, not the King in the North. It is extremely well-known in the North and there is even a popular song about it.