She was a mean professor -- maybe now we'll know why.
Author J.K. Rowling has published a new Harry Potter story today, Halloween, that provides a back story for Professor Dolores Umbridge. It was also released to Today Books, which posted it online.
In the Harry Potter films, Umbridge appeared as a sweet-looking lady in a pink dress. But she was in fact a sociopathic villain, who led a eugenics-like program against "muggles."
The story is free on Harry Potter's official website, Pottermore. It requires signing up as a member of the site, which is also free to do.