House Stark, one of the Great Houses in Westeros, was previously led by Lord Edward Stark. However, following his execution in King's Landing, the House fell into a period of instability, with Eddard's son Robb briefly leading the House and its vassals before his murder at the hand of the Freys. Jon Snow, Lord Eddard's adopted son, currently leads the House, and subsequently has control over The North.
House Lannister, one of the proudest and wealthiest Houses in Westeros, now hangs in the balance. Lord Tywin Lannister is dead at the hands of his own son, Tyrion. Tywin's eldest children, Jaime and Cersei, currently reside in King's Landing. Jaime, as a Knight of the Crown, has taken a vow to never marry or have children. Cersei, on the other hand, has lost all three of her children as a result of her desire to rule Westeros and claim the Iron Throne. For the time being, she sits upon that very throne, although enemies threaten her from both the North and the East.
House Targaryen ruled Westeros for over three centuries until Robert's Rebellion, a revolution that nearly wiped out the entirety of House Targaryen. Daenarys and Viserys, Aerys II Targaryen's only children to survive the war, were secreted away to Braavos. Now, Viserys has died and Daenarys has established herself as the ruler of Slaver's Bay. With her three dragons, Drogon, Rhaegal, and Viserion, by her side, Daenarys has finally set sail for Westeros, intent on reclaiming her throne.