Greyjoy Rebellion

The Greyjoy Rebellion was a brief uprising in the Seven Kingdoms of Westeros, fought between House Greyjoy, rulers of the Iron Islands, and the Iron Throne.

History
The rebellion took place nine years before the beginning of the series and was an attempt by House Greyjoy of the Iron Islands to break away and secure independence from the Iron Throne and revive the Old Way. Balon Greyjoy declared himself King of the Iron Islands and led the rebellion, supported by his vassals. The rebellion began eight years after King Robert I Baratheon seized the Iron Throne in the civil war known as Robert's Rebellion.

During the rebellion, House Greyjoy secured several early victories, including the burning of the Lannister fleet at anchor in Lannisport in a raid led by Euron and Victarion Greyjoy. They raided all along the western coast of Westeros, as far north as Sea Dragon Point. Their first major defeat came in an attempted attack on the coastal castle of Seagard. Balon's first son and heir, Rodrik, was killed in the failed assault.

However, the superiority of numbers and resources saw the Iron Throne crush the rebellion. The Greyjoy fleet was destroyed by Lord Stannis Baratheon. King Robert and his warden of the North Lord Eddard Stark besieged the Greyjoy stronghold of Pyke. The Iron Islands were outnumbered ten to one. During the final assault on Pyke, a battle-crazed warrior priest of the Lord of Light named Thoros of Myr led the way through a breach in the wall with his flaming sword, Jorah Mormont of Bear Island not far behind him. Eddard Stark and Jaime Lannister were also key fighters for the Iron Throne during the battle. Balon's second son, Maron Greyjoy, was killed in the fighting at Pyke. Maron's death was due to a collapsing tower during the battle.

The rebellion was crushed and Balon was forced to surrender. He was accepted back into the king's peace, keeping his lordship and titles, but only on the condition that his last surviving son Theon be made a ward of House Stark as hostage for his good behavior. Theon was just 8 years old at the time. Robert's victory cemented his hold on the throne, after having overthrown the Targaryens a few years before. King Robert knighted Jorah Mormont for his valor in the battle. Jory Cassel also fought in the Greyjoy Rebellion.

Season 1
Robert states that the Seven Kingdoms "haven't had a real fight in nine years", referring to the Greyjoy Rebellion.

Jory Cassel and Jaime Lannister reminisce about the Siege of Pyke, in which they were both fighting against the Greyjoys. Within this conversation they mention clearly remembering Thoros of Myr leading the way with a flaming sword. Also, Jory confirms that the scar on his face was obtained while fighting in the rebellion.

As he is leaving Winterfell, Tyrion Lannister tells Theon he remembers watching the Raid on Lannisport from Casterly Rock and that Theon's uncles were responsible.

In the books
In the A Song of Ice and Fire novels, the Greyjoy Rebellion took place five years after Robert Baratheon seized the Iron Throne and nine years before the events of the books. Lord Balon Greyjoy of the Iron Islands calculated that Robert's rule was as yet insecure and that many families would not go to war for a usurper. Balon declared independence from the control of the King on the Iron Throne. When Robert mobilized his armies, the ironborn launched several preemptive strikes, destroying the Lannister navy at anchor in the harbor of Lannisport and raiding the castle of Seagard, as well as many smaller attacks along the coast.

However, Stannis Baratheon and Paxter Redwyne, with their fleets from Dragonstone, Storm's End and the Arbor, defeated the ironborn fleet in a significant battle off Fair Isle. A large army assaulted the Greyjoy castle of Pyke, with the Red Priest Thoros of Myr and a brave Northman knight named Ser Jorah Mormont the first through the breach, both surviving to win high honor. Pyke was severely damaged and Lord Greyjoy's eldest two sons were killed before he finally surrendered and bent the knee. King Robert agreed to forgive Balon and restore him to the king's peace as long as his surviving son and heir Theon was given up to Lord Eddard Stark as hostage and a ward. Cersei Lannister regards her late husband's treatment of the Greyjoys as too lenient, and believes that her father's response to the rebellion would have been to give the ironborn a new island, made of their skulls.