He's gigantic, strong, and terrifying, but the Mountain that Rides has not been very accurately depicted on the show. Three different actors have played the Mountain in the show, and none have come close to matching the description of Ser Gregor from the books—but that's understandable given that any casting director would be hard-pressed to find an actor matching Clegane's unnatural stature, described as nearly 8 feet tall and 30 stone (420 lbs). Conan Stevens (7' tall) played Clegane in season one, followed by Ian Whyte (7'1") in season two. Whyte would go on to play the part of giant Wun-Wun, and the part of the Mountain has been played by Hafþór Júlíus Björnsson (6'9") ever since season four. While the shortest of the three actors to portray Clegane, Björnsson comes closest in appearance. As a strongman competitor, Björnsson has the heavily-muscled build we expect of Clegane.

So spake Martin: He was huge, the biggest man that Eddard Stark had ever seen. Robert Baratheon and his brothers were all big men, as was the Hound, and back at Winterfell there was a simpleminded stableboy named Hodor who dwarfed them all, but the knight they called the Mountain That Rides would have towered over Hodor. He was well over seven feet tall, closer to eight, with massive shoulders and arms thick as the trunks of small trees.... In the middle of the field, Ser Gregor Clegane disentangled himself and came boiling to his feet. He wrenched off his helm and slammed it down onto the ground. His face was dark with fury and his hair fell down into his eyes. – A Game of Thrones

"He is almost eight feet tall and must weigh thirty stone, all of it muscle. He fights with a twohanded greatsword, but needs only one hand to wield it. He has been known to cut men in half with a single blow. His armor is so heavy that no lesser man could bear the weight, let alone move in it." – A Storm of Swords

Show accuracy: 6/10 – I've given Björnsson a beefier build, including arms as thick as tree trunks. The Mountain also is supposed to have hair long enough to fall into his eyes, so I've given him a messy dark brown 'do.