The only other possible answer is Hermione Granger; I think it's a probably a toss-up between them. (Asher-Perrin undersells Hermione's importance by drawing the parallel to Lupin.)
I thought we'd all figured it out a long time ago?
Yup. Somewhere there is a parallel universe in which I read all about the exploits of Neville Longbottom. I'd totally read that. J.K. Rowling, stop dabbling in other things and take my money!