Which character is nicknamed "The Mountain" and played by Hafþór Júlíus Björnsson in the TV version of 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