We first met The Mountain when he killed Hugh of the Vale in a joust back in Season 1, then cut off his own horse's head in a rage against Loras Tyrell. He has quite the temper and any man who faces him is in for a difficult fight. read more
In the sixth season of the series, he is still referred to as Gregor Clegane, the Robert Strong name having been dropped entirely. While in the novels the murder of Rhaenys Targaryen is assigned to Ser Amory Lorch, another knight in the service of Tywin Lannister, the TV-series omitted this and Gregor is blamed for the death of Elia, Aegon and Rhaenys. read more
In a moment of rage Gregor then takes his horse’s head clean off for no reason and begins to attack Loras with his sword amidst the dead animal and showers of blood. read more