Theodor Seuss Geisel (pronounced /ˈɡaɪzəl/; March 2, 1904 – September 24, 1991) was an American writer and cartoonist most widely known for his children's books written under the pen name Dr. Seuss. He published over 60 children's books, which were often characterized by imaginative characters, rhyme, and frequent use of trisyllabic meter. His most celebrated books include the bestselling Green Eggs and Ham, The Cat in the Hat, and One Fish Two Fish Red Fish Blue Fish. Numerous adaptations of his work have been created, including eleven television specials, three feature films, and a Broadway musical.

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 U.S Army, where he wrote Design for Death, a film that later won the 1947 Academy Award for Documentary Feature.

Theodor Seuss Geisel was born on March 2, 1904, in Springfield, Massachusetts to Henrietta Seuss and Theodor Robert Geisel. His father, the son of German immigrants, managed the family brewery and after Theodor was married, supervised Springfield's public park system. Geisel was raised in the Lutheran faith and remained a member of the denomination his entire life. Geisel attended Springfield's Central High School and entered Dartmouth College in fall 1921 as a member of the Class of 1925 and joined Sigma Phi Epsilon fraternity. At Dartmouth, Geisel joined the humor magazine Dartmouth Jack-O-Lantern, eventually rising to the rank of editor-in-chief. Theo was his nickname. While at Dartmouth, Geisel was caught throwing a drinking party, violating national Prohibition laws of the time. As a result, the school insisted that he resign from all extracurricular activities. In order to continue his work on the Jack-O-Lantern without the administration's knowledge, Geisel began signing his work with the pen name "Seuss"; his first work signed as "Dr. Seuss" appeared after he graduated, six months into his work for humor magazine The Judge where his weekly feature Birdsies and Beasties appeared. At Dartmouth he was encouraged in his writing by professor of rhetoric W. Benfield Pressey, a beloved teacher who took a keen interest in Geisel's emerging talent.