Balon Greyjoy is the head of House Greyjoy of Pyke and is the Lord of the Iron Islands. The captain of the Great Kraken, he is a follower of the Old Way of the ironborn and desires to bring them back to prominence. Balon led the Iron Islands through to rebellion to claim their independence from the Iron Throne; both attempts failed the second with his untimely death.
Balon's first rebellion came a few years after Robert Baratheon claimed the Iron Throne. He hoped that Robert wouldn't have enough loyalty from his vassals to appropriately respond to the rebellion. Thanks to the newly constructed Iron Fleet. Balon had some initial success during the rebellion, such as when he burned the House Lannister fleet at anchor. However he was eventually defeated by the combined forces of Westeros and forced to bend the knee. His sole surviving son and heir, Theon Greyjoy was sent to House Stark as a ward to ensure Balon's good behaviour.
Balon would eventually commence a second rebellion upon the start of the War of the Five Kings and crowns himself the King of Salt and Rock. After refusing an alliance offer from Robb Stark which was presented by his son Theon Greyjoy, Balon commenced his Ironborn Invasion of the North. Before Balon's rebellion could get too far underway, Balon himself is killed under suspicious circumstances. He is succeeded by his brother, Euron Greyjoy who continues the Ironborn rebellion.