Source: wisegeek.com - Who is Dr seuss?
"He (Dr. Suess) crafted his first book, And to Think That I Saw It on Mulberry Street, in 1936, and 43 publishers rejected it."
"Dr. Seuss' rise to fame wouldn't begin for nearly 20 more years. In 1954, Life published a report about literacy
problems with school-aged children and cited that part of the problem
was that the available material was boring to kids. In fact, the
beginning readers of that time lacked zeal, especially when compared to
what would come. Inspired by this, Dr. Seuss worked with a list of 220 commonly seen words and wrote a story that contained them all. The result was The Cat in the Hat which achieved instant success and became one of the best known children's books of all time."
The article is worth reading, do visit it, if time is on your side :)