The Karstarks are descended from Karlon Stark, a younger Stark son who won lands a thousand years ago for putting down a rebellion. The Lord of Karhold, Lord Rickard is tall, gaunt, and fierce, with long hair and a long beard. He and his people tend to wear fur cloaks sewn out of pelts. Lord Karstark has several children, including three sons.
The hair and beard seem shorter, and the fur cloak is gone, but the actor seems a good fit. No mention is made of his sons, however, which is important to the character’s arc in the series.