"I had been writing for six months before she died and, the weird thing is, the essential plot didn't change after my mother died, but everything deepened and darkened," Rowling said. "Harry was always going to lose his parents. And it was always going to be a quest really to avenge them, but to avenge everyone against this, this creature -- this being who believes that he can make himself immortal by killing other people. So that's, that that's something I'd created before she died, but yes, its seeped into every part of the books. I think, in retrospect now I've finished I see just how much it informed everything."
After her mother's death, Rowling moved to Portugal to teach English as a foreign language. There, she married television journalist Jorge Arantes, with whom she had daughter, Jessica. But the marriage failed after two years and Rowling succumbed to depression.
"I had had a short and really quite catastrophic marriage and I'm left with this baby and I've got to get this baby back to Britain and I've got to rebuild us a life," Rowling recalled. "...Adrenalin kept me going through that and it was only when I came to rest that it hit me what a complete mess I had made of my life and that hit me quite hard."
Her deep depression inspired the creation of dementors, "the foulest creatures that walk this earth," who prey on people's happiness and suck out their souls in the Harry Potter series.
"I was definitely clinically depressed. And that's just characterized for me by, a numbness, just a sort of coldness and an inability to believe that you will feel happy again or that you could feel light-hearted again," she said. "It's just all the color drained out of life really."
The "Harry Potter" books may be located in an alternative fantasy world, but they address serious moral questions about the nature of trust, loyalty, integrity -- and the need to make a stand against evil.
Through the series, Harry Potter has to learn what it means to be a force for good against the dark arts of Lord Voldemort.
"I think we all understand what an act of evil is and Voldemort qualifies extravagantly for acts of evil," Rowling explained. "He has killed not out of self-defense, not to protect, not to do, not for any of the reasons that we might all be able to envisage. Most of could envisage ourselves killing in certain extreme situations if people we loved were threatened, or in war. He's killed cold-bloodedly, sometimes for enjoyment and for his own personal gain."
In November 2006, Rowling locked herself in the Balmoral Hotel in Edinburgh to work on the crucial final chapters of "Harry Potter and the Deathly Hallows" -- the final Harry Potter book. As the most anticipated new book of this century neared completion, it marked the end of a personal project for Rowling, who had been immersed in the magical world of Potter and her characters for seventeen years. With its completion, Rowling says it's time to focus on her family and her own well-being.
"I am happier now than I have ever been in my life, I am happier now than I was as a child, teenager, young adult and I think middle age is probably going to be my time," she said.
Watch "J.K. Rowling: A Year in the Life," Thursday, July 16 at 8 p.m. ET on ABC.