"If she hadn't died, I don't think it's too strong to say that there wouldn't be Harry Potter," Jo says. "The books are what they are because she died...because I loved her and she died."
Jo says she entered into a long period of depression after her mother's death. It was this struggle with depression that inspired one of the darkest aspects of the Harry Potter books—the Dementors, dark creatures who feed off of human happiness.
"It's so difficult to describe [depression] to someone who's never been there, because it's not sadness," Jo says. "I know sadness. Sadness is to cry and to feel. But it's that cold absence of feeling—that really hollowed-out feeling. That's what Dementors are."