Who is Victarion Greyjoy from A Feast for Crows and what is their importance?

Victarian Greyjoy is a great sea captain and brother of the former king Balon. Vicarian almost became king of the Iron Isles, but lost to his brother Euron because his niece decided to make her own bid for queen instead of throwing her voice with him. Victarian despises his brother for his betrayal.