The Cassels are household knights sworn to the Starks in Winterfell. Ser Rodrik Cassel, an old knight, is master-at-arms at Winterfell. He has only one daughter, young Beth. Jory Cassel, Ser Rodrik’s nephew and the captain of the household guard of Winterfell, is the son of Martyn Cassel, one of Lord Eddard Stark’s companions to the Tower of Joy who died there. Martyn fathered three other sons besides Jory, yet none of them lived to reach manhood.
Information about House Cassel that reveals spoilers from the books.