Gregor Clegane is five years older than his brother Sandor (I: 254)
At the age of 11 or 12, Gregor Clegane was nearly six feet tall and muscled like an ox. He was serving as a squire. When his younger brother stole a toy of his, he picked him up and held his face in a flaming brazier, disfiguring it permanently. It took three men to pull Gregor off of his young sibling, but Gregor's father publicly said that Sandor's bedding had simply caught on fire (I: 254)
Gregor Clegane was knighted four years afterwards, receiving the accolade from Rhaegar Targaryen himself (I: 254)
Gregor Clegane was a new-made knight of seventeen years at the sack of King's Landing. Some say it was Clegane who dashed Aegon Targaryen against a wall, and it was whispered afterwards that he raped the princess Elia before putting her to the sword (I: 263)
Gregor Clegane was one knight amongst thousands when Greyjoy's Rebellion was put down (I: 263)
Dark rumors swirl around Clegane. Two of his wives had died mysteriously, the keep is so grim that the dogs fear to enter the hall, and servants disappear unaccountably (I: 263)
Clegane's sister died young under strange circumstances, the fire that had disfigured his brother Sandor was seen as strange, and a hunting 'accident' took the life of Gregor Clegane's father. When he inherited the estate, his brother Sandor left immediately never to return, taking service with the Lannisters (I: 263)
The banner of the Cleganes is three black dogs on a yellow field (I: 572)
It is common knowledge in Casterly Rock that Gregor Clegane killed Elia Targaryen and her young son, and it is said that he raped the princess with the blood and viscera of her child on his hands (II: 203)
Sandor Clegane's grandfather was the founder of the house. He served as kennelmaster in Casterly Rock. One autumn the Lord Tytos was nearly killed by a lioness, but Clegane came up with his hounds and saved him. Three dogs died, and Sandor's grandfather lost his leg. In gratitude, Tytos Lannister gave him a towerhouse and lands and took his son to squire (II: 211)
The Clegane arms were chosen to memorialize the incident that raised up the family's fortunes. The three dogs on the yellow field recall the three hounds that died on the autumn grass (II: 211)
Sandor Clegane was in Lord Tywin's host during the Sack of King's Landing (SSM: 1)
The Clegane lands are southeast of Lannisport (SSM: 1)