Here is a bit of trivia about Wicked. I heard the author of the book speak some years ago and he told how he came to write it. He said he was living in London and trying to become a writer but couldn't get a focus other than the wicked men of WWII. But then he remembered having to watch Wizard of Oz every year as a child and remembered the line when the twi withes met and the wicked said to Gilda "I might have known you were here" and then began to think along the lines of why two people who were raised the same and one turn out good and the other bad. That became the book and the later follow-up books.