The Battle of the Blackwater
Role: relief
Stannis Baratheon's fleet and army assaulted King's Landing. Tyrion Lannister's wildfire chain trap destroyed much of the fleet, and a last-minute relief force led by Tywin Lannister and Mace Tyrell shattered Stannis's army. The battle saved Joffrey's crown and cemented the Lannister-Tyrell alliance.
Robert's Rebellion
Role: late_entrant
The war that overthrew the Targaryen dynasty. Robert Baratheon, Eddard Stark, and Jon Arryn rebelled against King Aerys II after Prince Rhaegar abducted Lyanna Stark. The rebellion ended with Rhaegar's death at the Trident and the Sack of King's Landing.
The Sack of King's Landing
Role: commander
The final act of Robert's Rebellion. Tywin Lannister's army arrived at the gates professing loyalty to Aerys II, then turned on the city. Jaime Lannister killed the Mad King to prevent the wildfire plot, while Gregor Clegane murdered Princess Elia Martell and her children.