Tyrion Lannister
The entire episode is dedicated to the climactic Battle of the Blackwater, in which the Lannister army, commanded by acting Hand of the King Tyrion Lannister, defends the city of King's Landing as King Stannis Baratheon's fleet stages an attack at Blackwater Bay. Unlike all previous episodes, "Blackwater" does not follow the parallel storylines of the characters outside of King's Landing.