Theon Stark

King Theon Stark is an unseen character in Game of Thrones. He was King in the North during the Andal Invasion of Westeros.

Biography
When the Andals attempted to conquer the North, the unified northern lords under House Stark were able to keep them out, and King Theon sailed his own fleet to the Andal homeland Andalos for vengeance. There, he killed hundreds of Andal warriors, and upon returning to home, he placed their heads on spikes along the northern coasts as a warning to anyone attempting to conquer the North.

Reference

 * "Northern Allegiances to House Stark"