From A Wiki of Ice and Fire
Grey King fighting Nagga
|Reign||During the Age of Heroes|
|Other Titles||King of the Iron Islands|
|Royal House||House Greyjoy (Mentioned)|
The legends say the Drowned God himself helped the Grey King to slay sea dragon Nagga. From her bones he made his hall, the Grey King's Hall, which he heated with Nagga's living fire. For a thousand years he reigned. He took as his wife a mermaid and plotted his war against the Storm God.
He supposedly wore robes of woven seaweed and a tall pale crown made from Nagga's teeth. When the Grey King died, the Storm God snuffed out the fire and the sea stole his throne. Only his hall remains.