Theodor Seuss Geisel (/ˈɡaɪzəl/; March 2, 1904 – September 24, 1991) was an American writer and cartoonist. He was most widely known for his children's books, which he wrote and illustrated under the pseudonym Dr. Seuss. He had used the pen name Dr. Theophrastus Seuss in college and later used Theo LeSieg and Rosetta Stone.

Geisel published 46 children's books, often characterized by imaginative characters, rhyme, and frequent use of anapestic meter. His most-celebrated books include the bestselling Green Eggs and Ham, The Cat in the Hat, The Lorax, One Fish Two Fish Red Fish Blue Fish, The 500 Hats of Bartholomew Cubbins, Fox in Socks, The King's Stilts, Hop on Pop, Thidwick the Big-Hearted Moose, Horton Hatches the Egg, Horton Hears a Who!, and How the Grinch Stole Christmas!. His works have spawned numerous adaptations, including 11 television specials, four feature films, a Broadway musical and four television series. He won the Lewis Carroll Shelf Award in 1958 for Horton Hatches the Egg and again in 1961 for And to Think That I Saw It on Mulberry Street. Geisel also worked as an illustrator for advertising campaigns, most notably for Flit and Standard Oil, and as a political cartoonist for PM, a New York City newspaper. During World War II, he worked in an animation department of the United States Army, where he wrote Design for Death, a film that later won the 1947 Academy Award for Documentary Feature.