I've said it before, but it's worth saying again, so I believe I will!
Characters are people-they have names, likes and dislikes, and most importantly (and complex) a history.
We've all been through things that make us who we are today, and for each of my characters that is no different. They've lived and loved, cried and laughed, and fought and made-up. Each of us is a complex, three-dimensional (or more) human being, and so are the characters in a book.
So, how does one make a well-rounded character?
I'm sure there are many ways, but I've only got my way which is to interview them as though they are sitting right in front of me. I answer questions ranging from physical appearance to favorite colors and home life to make my characters as believeable as possible.
Here are some great interview forms I've found:
So happy character making...