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.