A notorious knight and retainer to House Lannister, he is well known for his enormous size, prowess in battle, extremely cruel nature, and uncontrollable temper.

After being mortally wounded in a duel with Oberyn Martell, he is resuscitated by Qyburn via sinister means and becomes member of the Kingsguard and the personal bodyguard of Cersei Lannister.

His enormous size and strength make him a fearsome warrior (in the novels he is nearly 8 feet (2.4 m)) tall, and weighs over 420 pounds (190 kg)), and he has earned a reputation for violence and brutality.

Gregor Clegane is not a point of view character in the novels, so his actions are witnessed and interpreted through the eyes of other people, such as Arya Stark and Cersei Lannister.

[4] In A Game of Thrones, Tywin Lannister sends him to raid the Riverlands in retaliation for Catelyn Stark's abduction of Tyrion.

When war breaks out, Gregor is given command of Tywin's vanguard and left flank and leads his men through intimidation.

He later abandons Harrenhal after slaughtering the prisoners and is defeated by Edmure Tully at the Stone Mill, but manages to escape back to the Westerlands.

Though Qyburn's treatment has changed his physical appearance and behavior, and seemingly made him completely mute, Qyburn explains that Ser Gregor - not naming him as such - has sworn a vow of silence and vowed to serve as Cersei's personal bodyguard until all her enemies are destroyed and evil has been driven from the realm.

He is confronted by his brother Sandor "The Hound" Clegane in the season finale, where Sandor conveys an ominous message that he (Gregor) already knows who is coming for him and that he has always known.Ser Gregor is present when Daenerys Targaryen arrives at King's Landing with all her forces, demanding the release of her advisor Missandei and Cersei's surrender.