Claim: Gregor Clegane is from a fictional kingdom called Westeros.

Ser Gregor Clegane , nicknamed The Mountain , is a fictional character in the A Song of Ice and Fire series of fantasy novels by American author George R. R. Martin , and its television adaptation Game of Thrones . He is a retainer to House Lannister . An enormous man , he is well known for his size , prowess in battle and cruelty .   Introduced in 1996 's A Game of Thrones , Gregor is the older brother of Sandor Clegane , from the fictional kingdom of Westeros . He subsequently appeared in Martin 's A Clash of Kings -LRB- 1998 -RRB- , A Storm of Swords -LRB- 2000 -RRB- and in A Dance with Dragons -LRB- 2011 -RRB- as Ser Robert Strong .   Ser Gregor Clegane is a huge knight and the elder brother of Sandor Clegane . Called `` The Mountain That Rides '' , he is known for his incredibly cruel nature and uncontrollable temper . His size and strength make him a fearsome warrior , and he has earned a reputation for cruelty and brutality . He is able to wield a two-handed sword one handed . When they were children , Gregor shoved Sandor 's face into a brazier , gruesomely scarring him .   Gregor Clegane is portrayed by Conan Stevens in season one , by Ian Whyte in season two , and by Hafþór Júlíus Björnsson in seasons four , five , and six in the HBO television adaptation .