House Greyiron of Orkmont is an exctinct house of the Iron Islands. The Greyirons were the High Kings of the islands during a thousand years.
For centuries, the High King of the Isles had been chosen between the lords and captains of the Iron Islands in a kingsmoot. Five hundred thousand years before the events described in A Song of Ice and Fire Urron Greyiron descended with his axemen among the ironborn assembled on Naga's Bones, murdering all their oponents and proclaiming himself king.
He also made the position hereditary, so at his death the Seastone Chair passed to his heir instead of being chosen. His line ruled during a thousand years until it was extinguished by the Andals that came to the Iron Islands.
According to non-canon letters from George R. R. Martin, his banner showed the sea king's head, white with dark green seaweed beard and hair, a black crown on a grey field.
The only known member of the house is Urron Redhand, who seized the throne by murdering all the other kings on the kingsmoot.