If you want the clue JKR put on her site, just ask, I already have it. With my own theories I might add.
Edit: I'll just post it anyway:
Quote:(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.