Ask someone "who is your favorite Harry Potter character" and you get a lot of different answers. I guarantee you that at LEAST half the time, their answer won't be Harry, Ron, or Hermione. I myself always answer with Sirius, Lupin, and Tonks, and sometimes Luna as well.
There are a good many things that irritated me about the last few books the first time I read them, but over break, I sat down and read the whole series again, a little more slowly than my usual breakneck-must-finish-book-NOW speed. And I realized that while there are some flaws to the books, in my mind at least, J K Rowling is astonishingly good at several things.
The first of course is world building, but that's a post for another day. What really struck me about the HP universe about two months ago was that Ms. Rowling works with a very large cast of characters. An almost astoundingly large cast. Think about it: you've got the three main characters, plus all the other Gryffindors, plus the other students at Hogwarts, plus the teachers, plus Ron's entire enormous family, plus the Order of the Phoenix, plus the Dursleys, plus the Death Eaters. That's a lot of people to keep track of, let alone make distinct, and yet somehow she does. Every single one of the Weasleys has his or her own completely developed personality. All of the teachers and adults are distinct and real (and in my opinion extremely awesome).
I think if I ever send her fan mail, I'm going to ask her how the heck she does such a good job with secondary characters. I can only hope she's got a form response about that.
I personally struggle with minor characters. I work in time periods where people would have had very large families, and yet Rose only has two siblings and Avar only has one. I worry about my secondary characters, that they're one-dimensional, that they're really only there for a specific purpose (or otherwise that people will wonder "what's he got to do with anything?").
I suppose what I ought to do is go through each of their motivations step by step, the way I did with Rose and Avar. After all, apparently Ms. Rowling has endless back story on some of those secondary characters that never made it into the books. Perhaps that's what makes them so real; the fact that she knows more about them than she shows us creates the idea of a real person on the page.
How do you go about writing secondary characters?