That's Sandor Clegane. The Hound.
Game of Thrones Season 4, Episode 10
You're going to be bigger than the Hound,
Game of Thrones Season 2, Episode 1
Hound, form a welcome party
for any Baratheon troop
Game of Thrones Season 2, Episode 9
If the Hound so much as
heard you mention it,
Game of Thrones Season 1, Episode 4
Ser Lancel, tell the Hound to tell the king
that the Hand is extremely busy.
Game of Thrones Season 2, Episode 9