Ramsay Bolton

Ramsay Snow, is an unseen character in the second season. The role has yet to be cast. He better known as "The Bastard of Bolton", is Lord Roose Bolton's bastard son and only living child. He stayed behind at the Dreadfort when his father left for the south to fight in the War of the Five Kings.

Season 2
Ramsay Snow besieges Winterfell in the name of King Robb Stark as ordered. He infuriates Theon Greyjoy - who currently holds the castle in the name of The Iron Islands and his father - by having a soldier blow a horn all through the night. In the morning of the next day, when Theon rallies his men to defend the castle, he is betrayed and knocked out cold by his men, who seem to take Rob Stark's offer of mercy for any Ironborn in the castle except Theon, as expected. However, the castle is mysteriously sacked afterwards.

In the books
Ramsay Snow is also Roose Bolton's bastard son in the books.