Did you know that the man who called himself Dr. Seuss once wrote ad campaigns for Standard Oil? Or that he started calling himself “Seuss” — not his last name — after he got in trouble at Dartmouth College?

Today is what would have been Dr. Seuss’s 98th birthday, and it is also, not coincidentally, Read Across America Day. The National Education Association and dozens of partners have been holding the annual reading day since 1998, when folks famous and not at all famous take time to read to children across the country. The goal: to encourage children to become lifelong readers.

Danny DeVito and Zac Efron read to school children in New York on Read Across America Day. (Charles Sykes/AP)

For some birthday trivia, here are six things you might not know about Seuss:

1. The first book that he wrote and illustrated, “And to Think That I Saw It on Mulberry Street,” was rejected by dozens of publishers (the number has varied in the story’s telling), and Seuss once said he thought about burning the manuscript before Vanguard Press published it in 1937.

John Fogarty of Creedence Clearwater Revival has reportedly said that the parade in the book influenced his song “Lookin’ Out My Front Door.”

2. His given name was Theodor Seuss Geisel, but he started using “Seuss” when he was a student at Dartmouth College and served as editor of the humor magazine, called Jack-o-lantern. He and some friends were caught drinking gin, and, as part of his punishment, he was told he could no longer edit and write for Jack-o-lantern.Geisel would have none of that, so he contributed cartoons and articles under pseudonyms, including T. Seuss and Seuss.

In 1927, he started calling himself “Dr. Theophrastus Seuss” as a joke, and then, the next year, made it simply, Dr. Seuss. He earned a bachelor’s degree at Dartmouth and went on to Oxford, where he began work on a doctorate but didn’t complete his studies.

3. He spent more than 15 years in advertising, designing campaigns for Standard Oil.

4. He learned the art of animation during World War II, when he made U.S. military training movies with director Frank Capra’s Signal Corps.

5. He wrote “The Cat in the Hat” when a publishing company asked him to write and illustrate a book that used 225 words that would be familiar to children who were new readers.

6. Dr. Seuss won a Pulitzer Prize, but not for any specific book. In 1984 he was given a Special Citation “for his special contribution over nearly half a century to the education and enjoyment of America's children and their parents.” He also had a hand writing for two Academy Award-winning documentaries.

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