Gregor Clegane appeared in what novel that  is the fifth novel in the series, "A song of Ice and Fire".
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". In the books, the character is initially introduced in 1996's "A Game of Thrones". He subsequently appeared in "A Clash of Kings" (1998), "A Storm of Swords" (2000) and in "A Dance with Dragons" (2011).
Game of Thrones (season 5) The fifth season of the fantasy drama television series "Game of Thrones" premiered on HBO on April 12, and concluded on June 14, 2015. It was broadcast on Sunday at 9:00 pm in the United States, consisting of 10 episodes, each running approximately 50–60 minutes. The season primarily adapts material from "A Feast for Crows" and "A Dance with Dragons", the fourth and fifth novels in George R. R. Martin's "A Song of Ice and Fire" series, though it also uses elements from the third novel, "A Storm of Swords", as well as the upcoming sixth novel "The Winds of Winter". It also contains original content not found in Martin's novels. The series is adapted for television by David Benioff and D. B. Weiss.