Louise Fitzhugh (October 5, 1928 - November 19, 1974) influenced me in a very unexpected way.
I got Harriet The Spy from my book club when I was about 10, and I didn't want to read it. I wasn't interested in books about girls. Because I liked writing stories, I thought the plot of this one sounded interesting, but I couldn't get past the fact that it was not only about a girl, but that the cover had her picture and her name.
Finally, one day, when I ran out of new books to read, I reluctantly cracked open Harriet The Spy. And I loved it, from the first sentence to the last, so much that I immediately read it again.
After that, even though I still preferred books about boys, I was less opposed to books about girls, as long as they did cool stuff like Harriet did.
I think about Harriet now and then, especially since this boy/girl thing has come full circle: I'm now (slowly) working on my first story with a girl main character.
Harriet the Spy received some criticism for containing characters who were less than admirable, but that's part of what made me love the book. It was almost like a grown-up book for kids. As it turns out, this is what made Fitzhugh so influential.
Her obit in the New York Times said it best: "The book helped introduce a new realism to children's fiction and has been widely imitated."