Board Thread:Questions and Answers/@comment-1031724-20160618003023/@comment-5014364-20160618164053

We're not even really sure in the books. It was vague if Gregor actually "died" and then was reanimated by Qyburn, or if he was dying. Qyburn is rumored to have mis-used his medical knowledge - gained from dissecting living people - to learn some sort of necromancy. He's a mad scientist (though he's not actually insane, he genuinely believes that pushing the boundaries of "science" will help society as a whole).

In the books, it's even somewhat implied that he doesn't have a head - they send Gregor's skull to the Martells as proof of his death. The question is....was that really his skull, or was it a fake they made from someone else?

In the books he wears a helmet that totally covers his face and eyes, you see (probably too difficult for the stunt man given that he needs to see on set).

In the books they never actually say it's Gregor, they call him "Robert Strong", but it's sort of an open secret - there's only so many 8 foot tall men in Westeros, everything thinks it's Gregor.

FrankenGregor terrifies everyone at court; the other Kingsguard point out that they never see him take off his armor - even to eat, drink, or use the privy. Kevan thinks to himself that dead men don't need to do those things. Another points out that he's just...around ALL THE TIME - he never seems to sleep.

And he's clearly vastly stronger than Gregor ever was in life before.