Ser Rickard Karstark from A Storm of Swords is a bannerman to Robb Stark and Winterfell. Because of the death of his son he takes it upon himself to kill the two boys (Lannister and Frey children) in revenge, even though Robb has forbidden it, hoping to use the boys as a hostage exchange for his sisters. Because he defied his orders, Robb has to execute Karstark. This sets up a fued between the Starks and the Karstarks.
