The Mountain Got Actor Change. Due to his incredibly massive size he is called the mountain that rides or more often simply the mountain after being poisoned in a duel with oberyn martell gregor almost. Throughout the series the mountain has been played by 3 actors.

He turned out to be too expensive and left game of thrones for the hobbit. The mountain was less visible in season two but when he did appear he was played by the welsh actor ian whyte as he tried to determine who made an attempt on tywin lannister s life. The two actors look very similar so it would have been easy for fans to completely miss this change up in faces.
The actor appeared in two episodes but he was later recast ahead of season 2 because of scheduling conflicts.
Ser gregor clegane was a knight of house clegane the older brother of sandor clegane and a notoriously fearsome extremely lethal and much feared warrior with a tendency toward extreme and excessive violence. Here are 9 times game of thrones recast characters. The mountain was less visible in season two but when he did appear he was played by the welsh actor ian whyte as he tried to determine who made an attempt on tywin lannister s life. He turned out to be too expensive and left game of thrones for the hobbit.