According to Archmaester Eyron, the Marsh King was a "first among equals", often thought to be touched by the old gods. Songs claim the Marsh Kings rode lizard-lions and wielded frog spears. Marsh Kings held Moat Cailin against southron invaders, sometimes with the assistances of the Barrow Kings, Red Kings, or Kings of Winter.
Thousands of years ago, Rickard Stark, the King in the North, killed the last of the Marsh Kings and married his daughter, thus annexing the Neck to the realm of Winterfell. The Neck has since been ruled by House Reed of Greywater Watch; it is unknown if they have a connection with the ancient Marsh Kings.