Dagmer

"You want to keep a man silent, you silence him."

- Dagmer to Theon, referring to a farmer and his family that he murdered.

Dagmer is a character from A Song of Ice and Fire/Game of Thrones.

He is ironborn captain the Foamdrinker, while in the HBO tv series he's the first mate of the Sea Bitch.

He takes orders from Balon Greyjoy and helps Theon Greyjoy on a raid to harry the Stony Shore then later to take Winterfell along with his men.

A Clash of Kings
Dagmer is defeated by Ser Rodrik Cassel in the Battle of Torrhen's Square. According to Asha Greyjoy, Dagmer returned to Torrhen's Square and took the castle after the Stark forces returned to free Winterfell.

Season 2
In the tv series Dagmer is much more cruel and dangerous and takes role and actions of Ramsay Snow, who's not present in the season unlike the book. Dagmer's actions at Winterfell in the TV series, such as telling Theon to kill to display dominance, murdering the orphan boys to pass off as Bran and Rickon, and later betraying Theon, in the books were all suggested by Ramsay Snow, who at the time was pretending to only be a Bolton servant named "Reek". He murder two married farmers and their children.

Later Dagmer betrays Theon and stabs Maester Luwin. After handing Theon over, Dagmer and his men are flayed alive by Ramsay Snow and the soldiers of House Bolton.