Theodor Seuss Geisel ( sooss GHY-zəl, zoyss -⁠; March 2, 1904 – September 24, 1991) was an American children's author, illustrator, animator, and cartoonist. He is known for his work writing and illustrating more than 60 books under the pen name Dr. Seuss ( sooss, zooss). His work includes many of the most popular children's books of all time, selling over 600 million copies and being translated into more than 20 languages by the time of his death.

Geisel adopted the name "Dr. Seuss" as an undergraduate at Dartmouth College and as a graduate student at Lincoln College, Oxford. He left Oxford in 1927 to begin his career as an illustrator and cartoonist for Vanity Fair, Life, and various other publications. He also worked as an illustrator for advertising campaigns, including for Flit and Standard Oil, and as a political cartoonist for the New York newspaper PM. He published his first children's book And to Think That I Saw It on Mulberry Street in 1937. During World War II, he took a brief hiatus from children's literature to illustrate political cartoons, and he worked in the animation and film department of the United States Army.

After the war, Geisel returned to writing children's books, writing acclaimed works such as If I Ran the Zoo (1950), Horton Hears a Who! (1954), The Cat in the Hat (1957), How the Grinch Stole Christmas! (1957), Green Eggs and Ham (1960), One Fish, Two Fish, Red Fish, Blue Fish (1960), The Sneetches and Other Stories (1961), The Lorax (1971), The Butter Battle Book (1984), and Oh, the Places You'll Go! (1990). He published over 60 books during his career, which have spawned numerous adaptations, including eleven television specials, five feature films, a Broadway musical, and four television series.

He received two Primetime Emmy Awards for Outstanding Children's Special for Halloween Is Grinch Night (1978) and Outstanding Animated Program for The Grinch Grinches the Cat in the Hat (1982). In 1984, he won a Pulitzer Prize Special Citation. His birthday, March 2, has been adopted as the annual date for National Read Across America Day, an initiative focused on reading created by the National Education Association.