History
Gregor “the Mountain” Clegane is the older, bigger, meaner brother of Sandor “the Hound” Clegane. We first met Gregor in season 1, where he was an enormous, bloodthirsty jackass. He kept that up for several years until his fight with Oberyn Martell brought him to the brink of death in season 4. Qyburn the disgraced maester saved Gregor from the grave by turning him into a Frankenstein’s monster-like abomination. He now serves as Cersei’s hulking bodyguard.
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Status
We don’t know what, if anything, is going on in Gregor’s mind, but we know he’s crazy huge, stupid strong, and lives to serve the vengeful Cersei Lannister. If she so chooses, Cersei could do a lot of damage by pointing Gregor in the direction of an enemy and taking him off the leash.
Gregor also has a longstanding feud with his brother Sandor (he gave the Hound his disfiguring facial scar), although it’s unclear if he still cares about such things in his new, zombie-esque state. In any case, fans have wanted to see these two face off for a while. Will we finally get a Clegane family showdown in season 7?