The master-at-arms at Pyke and captain of the longship Foamdrinker, Cleftjaw is named for the horrific scar that nearly splits his face, making his smile a disconcerting and ugly thing. Now old, his name is still feared. He personally taught Theon Greyjoy before he was taken away as a hostage to Winterfell, and Theon calls him “uncle”. The actor cast in the role is much younger than the actual character in the novel, clearly is not playing as if he and Theon know one another, and his horrific scar has been reduced to something much less significant.
Dagmer serves as Theon’s right hand when Lord Balon sends Theon to attack the North. When Theon goes on to take Winterfell, Dagmer is with him. After Bran and Rickon escape custody, it is Dagmer who suggests to Theon that they kill two innocent farm boys and claim that they are Bran and Rickon so as to cow the inhabitants of the castle. However, when the northerners give Theon an ultimatum to surrender, and offer amnesty to any who lay down their arms, Dagmer personally knocks Theon unconscious. He and the other ironmen drag Theon away to turn him over to the northmen.