Gelmarr

Gelmarr is a background character in the second season. He is played by an unidentified extra and debuts in "The Ghost of Harrenhal" though first identified in "Valar Morghulis". Gelmarr is an ironborn raider and member of the Sea Bitch crew.

In the books
In the Song of Ice and Fire novels, Gelmarr's background is the same. He's also known as "Gelmarr the Grim" and took part in the raid of Stony Shore, the assault on Winterfell and the hunt for Bran and Rickon. Alongside Aggar, he was present during the execution of the children whose corpses were passed off as Bran's and Rickon's. He's later killed by the manservant known as "Reek" to keep the secret of the corpses' true identities.