Remus/Hannah
Professor Quirrell. He was there my first year. Fourth-year was Mad-Eye Moody, but he wasn't really Moody. It was a Death Eater using a Polyjuice potion. Then my seventh year we had another Death Eater, Amycus Carrow.
Yes, I know what you are. It's called Wolfsbane Potion, created by Damocles Belby. It won't cure lycanthropy but eases the symptoms, you're still you in your head. From what I've read, most will still find a safe space and sleep during the full moon.