Robb Stark is the eldest son of Ned and Catelyn Stark and thus the heir of Winterfell.  He takes control of the North in his father's absence.

Robb Stark Quotes

Theon: You're afraid?
Robb: I must be.
Theon: Good.
Robb: Why is that good?
Theon: It means you're not stupid.

Tyrion: I must say I received a slighter warmer welcome on my last visit.
Robb: Any man of the Night's Watch is welcome at Winterfell.
Tyrion: Any man of the Night's Watch but not I, eh boy?
Robb: I'm not your boy, Lannister. I'm Lord of Winterfell while my father is away.
Tyrion: Then you might learn a Lord's courtesy.

Game of Thrones Quotes

Tyrion: Let me give you some advice bastard. Never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you.
Jon: What the hell do you know about being a bastard?
Tyrion: All dwarfs are bastards in their father's eyes.

I will hurt you for this. A day will come when you think you are safe and happy, and your joy will turn to ashes in your mouth. And you will know the debt is paid.

Tyrion Lannister