In the world of Game of Thrones, House Targaryen ruled the Seven Kingdoms in Westeros for nearly three hundred years. The last Targaryen to serve as King was Aerys II, often referred to as the Mad King, and he ruled for about 20 years – from 262-283 AC.
By the time the story of Game of Thrones began, Robert Baratheon sat upon the Iron Throne in the Red Keep of King's Landing, the capital city of Westeros. Fans may remember many instances in which the characters talked about how Robert came to be the King, but the tale of Robert's Rebellion, also known as the War of the Usurper, was never actually shown in the TV series.
In a sort of snowball effect chain of events, Robert Baratheon – aided by a few of his loyal companions – overthrew Aerys II from the Iron Throne in a rebellion that is said to have lasted "close to a year". With battles ensuing all across Westeros, which ended with the Mad King being slain in his own royal abode, Robert's Rebellion would be the event that ended House Targaryen's rule and thus begin the narrative that is Game of Thrones.
What Was Robert's Rebellion in Game of Thrones?
Robert's Rebellion refers to the events and battles that led to the overthrowing of King Aerys II Targaryen. It all started with a grand festival held in Harrenhal, which would come to be known as Lord Whent's Great Tournament. At this tourney, which took place in 281 AC, there was a jousting match in which the son of Aerys II, Prince Rhaegar Targaryen, was the victor and given the opportunity to crown the new queen of love and beauty.
Traditionally, the winner would bestow the crown of blue roses to his wife or love interest, which in Rhaegar's case, would've been his wife Elia Martel. Instead, Rhaegar gave the crown to Lyanna Stark of Winterfell, who was betrothed to Robert Baratheon of Storm's End. This caused much controversy among the people and soon thereafter, Rhaegar and Lyanna were both gone without a trace, leading many to believe Rhaegar had kidnapped the Lady of Winterfell.
While Lyanna's brother, Brandon Stark, was making his way to Riverun to marry Catelyn Tully, he heard of his sister's apparent kidnapping and rushed to King's Landing where he shouted for Rhaegar at the Red Keep, demanding he come out and fight for his life against the mighty northman. However, Rhaegar was not in King's Landing, rather, the Mad King heard of Brandon's demands from outside the Keep, and ordered his guards to capture and imprison Stark and his men.
With the northerners held captive, Aerys summoned Brandon's father, Rickard Stark, to answer for his son's crimes in plotting the murder of the Targaryen Prince. Rickard arrived and demanded a trial by combat, to which Aerys granted. However, while Rickard chose himself as his own champion to fight, Aerys chose fire as his and ordered his men to burn Rickard alive. In an attempt to rescue his father, Brandon strangled himself to death while being held in a contraption that tightened around his neck the further he tried to move away from it. All who accompanied both Brandon and Rickard were presumably executed.
Aerys then called upon Lord Jon Arryn of the Vale to bring him the heads of Eddard Stark and Robert Baratheon, who he suspected would seek justice for the deaths of the many northmen. But Jon decided against the King's wishes and stood by his fellow brethren, raising his banners in rebellion to fight alongside House Stark and House Baratheon against the Mad King and House Targaryen.
After many battles won at the hands of the rebellion, the Iron Throne was overthrown and Aerys II was slain by none other than a member of his own Kingsguard, Ser Jaime Lannister, preparing Robert Baratheon to take the throne for himself and be the next Lord of the Seven Kingdoms.
Who Fought Alongside Robert Baratheon?
Among the rebels who fought to overtake the throne alongside House Baratheon were House Stark and House Tully. House Arryn was divided in the war, with some siding with the rebellion – including Jon Arryn – and others staying loyal to the crown.
Another complication in loyalty was within House Lannister. Before the rebellion, the Lord of Casterly Rock, Tywin Lannister, served as Hand of the King for many years to Aerys II. He was very effective as the Hand and provided economic prosperity among Westeros. But as the King became more and more unstable, he grew jealous of Twin and would belittle his accomplishments. Tywin was unfazed until Aerys appointed Tywin's son Jaime, the heir to House Lannister, to the Kingsguard, stripping him of his title as heir. Enraged, Tywin resigned his position as Hand of the King and returned to Casterly Rock.
While the rebellion was occurring, Tywin decided to not take a side and remained neutral until the war was over. Fans of the show and books know that he then took the opportunity to betroth his daughter, Cersei, to Robert once he became king, thus making the Lady of Casterly Rock the Queen.
Who Fought Against Robert's Rebellion?
In addition to the members of the Vale who stood by the crown, the Houses of Tyrell and Martell remained loyal to House Tagaryen and fought against Robert and his great rebellion. Within the many battles that ensued, the Houses of Grafton, Grandison, Cafferen, and Fell attempted to end the rebellion, but to no avail.
Eventually, Rhaegar returned in a final stand against the rebels and fought Robert himself in the Battle of the Trident in the riverlands. Rhaegar managed to wound the future king but was ultimately killed by Robert's Warhammer. The Game of Thrones would then begin once Robert took the throne.