In this parody version by YouTube user GrombarSmash, that character is Gregor Clegane, a knight with a reputation for violence extreme even by the standards of Westeros nobility. Here is "Bannerman," a tale of a bloodthirsty killer:
Sack us a town, you're the bannerman.
Sack us a town tonight.
'Cause you're big, and you're strong, and you're merciless.
And you love setting buildings alight.
Content warning: violence, gore, and scenes from Season 1.
-via Geek Art Gallery