I think I'm gonna have to give the honour to Roald Dahl's Matilda. Matilda was the first character I completely identified with - like me, she loved to read and like me, she didn't fit in with the rest of her family. I was a lonely child and reading Matilda made me realise that I could find friends in books.
Matilda was also something of a role model for me. Not for her telekinetic powers (although I did spend a lot of time trying to move a carrot with my mind), but because of the way she changed her own life. I would have loved to find my own Miss Honey as a child and while it never happened for me, it's part of the reason I became a teacher - so I could be Miss Honey to someone else.