Professor Alastor "Mad-Eye" Moody (Brendan Gleeson)
The man we think is Mad-Eye Moody for most of the film turns out to be Barty Crouch Jr. in disguise. The real Mad-Eye only appears in one flashback and then at the very end, locked in a trunk in his own office. (Talk about adding insult to injury.)
Regardless, we know a few things about the Mad-Eye himself, such as:
His nickname comes from his magical fake eye, which replaced a real one he lost doing something dangerous.
Oh yeah, and on that front: he's known as pretty tough, and very good at catching bad guys. Ron pretty much sums him up for us early in the film:
RON: Dark-wizard catcher. Half the cells in Azkaban are filled thanks to him.
So, yeah, he seems like an impressive guy. Too bad we didn't get to see more of him as him. Maybe in the next installment, eh?