'Game of Thrones' photo: Season 4's Mountain, Hafthor Julius Bjornsson
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The character of Gregor Clegane, known as the Mountain because of his intimidating size, has previously been played by two other actors, Conan Stevens (in Season 1) and Ian Whyte (in Season 2). The Mountain did not appear in 2013's Season 3.
Note: Gregor Clegane is a notoriously awful person and will not likely have such a nice smile in "Game of Thrones."
Season 4 of "Game of Thrones" will air on HBO in the spring of 2014.