<P> 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, six, and seven . </P> <P> 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 Cersei Lannister . Gregor is mostly a background character in the novels . </P> <P> In A Game of Thrones, Tywin Lannister sends him to raid the Riverlands in retaliation for Catelyn Stark's abduction of Tyrion . Beric Dondarrion is sent to arrest Gregor, but Gregor ambushes and kills him . He and his men continue raiding the Riverlands throughout A Clash of Kings . When Tyrion Lannister demands a trial by combat, the accuser Cersei Lannister chooses Gregor as her champion . Elia's brother Oberyn Martell is named Tyrion's champion for his own agenda to expose Gregor as a murderer . Oberyn wounds him with a poisoned spear, but the Mountain is ultimately victorious as he admits to murdering Elia and Aegon before crushing Oberyn's skull . Gregor's body is given to Qyburn for experimentation and he is reported to be dead with his head sent to Dorne as a peace offering to Doran Martell in the wake of his brother's death . But following Cersei's walk of atonement, she gains a bodyguard named Ser Robert Strong who is of similar enormous stature as Gregor, and whose body is completely covered in armor . </P> <P> In Season 1, Tywin Lannister sends him to raid the Riverlands . Beric Dondarrion is sent to arrest Gregor . When war breaks out, Gregor is given command of Tywin's vanguard and left flank and leads his men through intimidation . </P>

When does the mountain first appear in game of thrones
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