when i first read the books, four people came to mind instantly. Alan Rickman as Snape, just reading the characterisation in the books reminded me of an early role of his. Slope in the Barchester Chronicles. I alwys thought JK must have watched that tv series and got the idea for Snape. Maggie Smith for Prof McGonagle, Robbie Coltrane for Hagrid and much later Imelda Staunton for Umbridge. I love the young Daniel's reaction to working with Mr Rickman.