Rickard Karstark is the Lord of Karhold, which is northeast of the Dreadfort. His Banner is a (rising (?)) Sun on white Background.
He is a vassal of King Robb Stark of The North. His relatives are (among others):
Harrion Karstark (son)
In the Books he is one of the mightiest Bannermen of the Starks, together with Roose Bolton.