Hafþór Júlíus "Thor" Björnsson, is an Icelandic professional strongman, actor, and former professional basketball player, he plays which 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"?
Hafþór Júlíus Björnsson:  He plays Ser Gregor "The Mountain" Clegane in the HBO series "Game of Thrones". Gregor Clegane: Gregor Clegane, nicknamed "The Mountain That Rides" or simply "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".
Gregor Clegane