Martyn Lannister

Martyn Lannister is a character in the third season. Along with his brother Willem, he is a squire in the Lannister army. Both are younger sons of Kevan Lannister, and younger brothers of Ser Lancel Lannister.

Season 3
Martyn, along with his brother Willem, is captured by the forces of House Tully led by Edmure Tully following the Battle of Stone Mill. He's taken hostage and placed in a cell at Riverrun, the seat of the Tullys.

After Robb Stark visits Riverrun to attend the funerals of Lord Hoster Tully, Martyn and Willem are visited in their cell by Queen Talisa Stark, who tends to Martyn's wounded hand while Willem looks in silence. Martyn asks if its true that Robb can turn into a wolf at night and devours the flesh of his enemies.

Martyn and Willem are murdered inside their cells by Lord Rickard Karstark.

Behind the scenes
Martyn is played by Dean-Charles Chapman, who would go on to be cast as Tommen Baratheon in the fourth season of the television series.

In the books
In the A Song of Ice and Fire novels, Martyn and Willem are the twin sons of Ser Kevan Lannister, and younger brothers of Lancel Lannister. Martyn is captured at the Battle of Oxcross. It is not Martyn but his cousin Tion Frey who is killed with Willem by Rickard Karstark. After Willem and Tion's death, Robb ordered to triple the guard on Martyn for his protection, and later exchanged him for a northman prisoner (Robett Glover). Martyn is not mentioned in the books afterwards.