Willy Ley (sometimes credited as Willie Ley) was a German-American science writer and space advocate who helped popularize rocketry and spaceflight in both Germany and the United States. The crater Ley on the far side of the Moon is named in his honor.
I absolutely devoured this book. The combination of legend and science was irresistible. (I'm writing this in long retrospect; I estimate I was in jr. hi. when I first read it.)