What happened to Tom (The barman) in the Harry Potter series?

In 1991, Tom the barman looked completely normal when Hagrid first brought Harry into the Leaky Cauldron, he had hair, he stood up straight and he spoke normally. Then suddenly in the later films he was portrayed as a hunchback and acted kind of strangely. I don't recall any details noting this change in the books, I do remember a passage describing him as being quite bald, toothless and is comparable to a "gummy walnut" though, maybe the first film just portrayed him wrong since there was no physical description of Tom in the first book? I'm not sure, but it bothers the hell out of me, lol, what are your thoughts on this?