After graduating from Dartmouth College (B.A., 1925), Geisel did postgraduate studies at Lincoln College, Oxford, and at the Sorbonne. He subsequently began working for Life, Vanity Fair, and other publications as an illustrator and humorist. In addition, he found success in advertising, providing illustrations for a number of campaigns. Geisel was especially noted for his work on ads for Flit insect repellent.

After illustrating a series of humour books, Geisel decided to write a children’s book, which was reportedly rejected by nearly 30 publishers. After his chance meeting with a friend who was an editor at Vanguard Press, And to Think That I Saw It on Mulberry Street was finally released in 1937. The work centres on a young boy who transforms his ordinary walk home from school into a fantastical story. Later, however, he describes only the facts of his walk to his father, who frowns on the boy’s imaginative nature. Geisel used the pen name Dr. Seuss, the Dr. was a tongue-in-cheek reference to his uncompleted doctorate degree.

After publishing several more children’s works, Geisel released Horton Hatches the Egg in 1940. With it, he introduced the features that would come to define his books: a unique brand of humour, playful use of words, and outlandish characters. It centres on an elephant who is duped into sitting on the egg of a bird who goes on vacation. Despite various hardships, Horton refuses to leave: “I meant what I said, and I said what I meant. An elephant’s faithful one hundred percent!” In the end, he is rewarded when the egg hatches, and a creature with bird wings and an elephant’s head emerges.

In 1947 Geisel published  McElligot’s Pool, about a boy who imagines a fantastical marine world while fishing. The work was especially noted for Geisel’s inventive creatures, which would come to populate his later stories. In addition, he continued to use his whimsical rhymes to convey important life lessons. In Horton Hears a Who! (1954), the loyal pachyderm returns to protect a tiny speck of a planet known as Whoville. A discussion about minority rights and the value of all individuals, the work features Horton repeating “a person’s a person, no matter how small.”

In 1957 Geisel published two of his most popular works: The Cat in the Hat and How the Grinch Stole Christmas!. The former features a mischievous talking cat who entertains two bored children on a rainy day, while the latter introduces the Scrooge-like Grinch, who wants to ruin Christmas in Whoville but ultimately discovers that the holiday is more than just its material trappings. How the Grinch Stole Christmas! was later adapted (1966) for television, and it became a holiday staple.

In 1958 Geisel founded Beginner Books, Inc., which in 1960 became a division of Random House. He subsequently wrote a number of books for beginning readers, notably One Fish Two Fish Red Fish Blue Fish (1960), Green Eggs and Ham (1960), Hop on Pop (1963), and Fox in Socks (1965).

They—along with his other works—went far beyond the traditional, and often boring, primers and were valued for their contribution to the education of children. During this period, Geisel also wrote The Lorax (1971), in which he expressed concern for the environment. The cautionary tale centres on a businessman who destroys a forest of Truffula trees—despite the protest of the Lorax, who speaks up because “the trees have no tongues”—and, when left with a desolate landscape, laments the damage he has caused.

Giesel’s later notable books include the inspirational Oh, the Places You’ll Go! (1990), which became a popular graduation gift.

In 1984 Geisel received a special Pulitzer Prize “for his special contribution over nearly half a century to the education and enjoyment of America’s children and their parents.” The honour underscored the immense popularity of his works, which were perennial best sellers. According to various reports, by the early 21st century more than 600 million copies of Dr. Seuss books had been sold worldwide.

According to britannica.com