Well this is the excerpt from book 6
"He looked rather like an old lion. There were streaks of grey in his mane of tawny hair and his bushy eyebrows; he had keen yellowish eyes behind a pair of wire-rimmed spectacles and a certain rangy, loping grace even though he walked with a slight limp."
my vote that this guy is the new dada teacher. . .or maybe the half-blood prince himself?