He began submitting humorous articles and illustrations to Judge (a humor magazine), The Saturday Evening Post, Life, Vanity Fair, and Liberty. One notable "Technocracy Number" made fun of Technocracy, Inc. and featured satirical rhymes at the expense of Frederick Soddy. He became nationally famous from his advertisements for Flit, a common insecticide at the time. His slogan, "Quick, Henry, the Flit!" became a popular catchphrase. Geisel supported himself and his wife through the Great Depression by drawing advertising for General Electric, NBC, Standard Oil, and many other companies. He also wrote and drew a short lived comic strip called Hejji in 1935.
Even at this early stage, Geisel had started using the pen name "Dr. Seuss". His first work signed as "Dr. Seuss" appeared six months into his work for Judge. Seuss was his mother's maiden name; as an immigrant from Germany, she would have pronounced it more or less as "zoice" (as it is pronounced in German), but today it is universally pronounced in English with an initial s sound and rhyming with "juice". The "Dr." is an acknowledgement of his father's unfulfilled hopes that Seuss would earn a doctorate at Oxford. Geisel also used the pen name Theo. LeSieg (Geisel spelled backwards) for books he wrote but others illustrated.
In 1936, while Seuss sailed again to Europe, the rhythm of the ship's engines inspired the poem that became his first book, And to Think That I Saw It on Mulberry Street. Seuss wrote three more children's books before World War II (see list of works below), two of which are, atypically for him, in prose.
As World War II began, Dr. Seuss turned to political cartoons, drawing over 400 in two years as editorial cartoonist for the left-wing New York City daily newspaper, PM. Dr. Seuss's political cartoons opposed the viciousness of Hitler and Mussolini and were highly critical of isolationists, most notably Charles Lindbergh, who opposed American entry into the war. Some cartoons depicted Japanese Americans as traitors. One of these appeared days before the internments started. Some have taken these cartoons to reflect his own negative attitude toward the Japanese people, while others have taken him to be presenting a parody of others' attitudes.
In 1942, Dr. Seuss turned his energies to direct support of the U.S. war effort. First, he worked drawing posters for the Treasury Department and the War Production Board. Then, in 1943, he joined the Army and was commander of the Animation Dept of the First Motion Picture Unit of the United States Army Air Forces, where he wrote films that included "Your Job in Germany," a 1945 propaganda film about peace in Europe after World War II, "Design for Death," a study of Japanese culture that won the Academy Award for Best Documentary in 1947, and the Private Snafu series of very adult army training films. While in the Army, he was awarded the Legion of Merit. Dr. Seuss's non-military films from around this time were also well-received; Gerald McBoing-Boing won the Academy Award for Best Short Subject (Animated) in 1950.
Despite his numerous awards, Dr. Seuss never won the Caldecott Medal nor the Newbery. Three of his titles were chosen as Caldecott runners-up (now referred to as Caldecott Honor books): McElligot's Pool (1947), Bartholomew and the Oobleck (1949), and If I Ran the Zoo (1950).
After the war, Dr. Seuss and his wife moved to La Jolla, California. Returning to children's books, he wrote what many consider to be his finest works, including such favorites as If I Ran the Zoo, (1950), Scrambled Eggs Super! (1953), On Beyond Zebra! (1955), If I Ran the Circus (1956), and How the Grinch Stole Christmas! (1957).
At the same time, an important development occurred that influenced much of Seuss's later work. In May 1954, Life magazine published a report on illiteracy among school children, which concluded that children were not learning to read because their books were boring. Accordingly, Seuss's publisher made up a list of 400 words he felt were important and asked Dr. Seuss to cut the list to 250 words and write a book using only those words. Nine months later, Seuss, using 220 of the words given to him, completed The Cat in the Hat. This book was a tour de force—it retained the drawing style, verse rhythms, and all the imaginative power of Seuss's earlier works, but because of its simplified vocabulary could be read by beginning readers. A rumor exists, that in 1960, Bennett Cerf bet Dr. Seuss $50 that he couldn't write an entire book using only fifty words. The result was supposedly Green Eggs and Ham. The additional rumor that Cerf never paid Seuss the $50 has never been proven and is most likely untrue. These books achieved significant international success and remain very popular.
Dr. Seuss went on to write many other children's books, both in his new simplified-vocabulary manner (sold as "Beginner Books") and in his older, more elaborate style. The Beginner Books were not easy for Seuss, and reportedly he labored for months crafting them.
At various times Seuss also wrote books for adults that used the same style of verse and pictures: The Seven Lady Godivas, Oh, The Places You'll Go!, and his final book You're Only Old Once, a satire of hospitals and the geriatric lifestyle.
During a very difficult illness, Helen Palmer Geisel committed suicide on October 23, 1967. Seuss married Audrey Stone Diamond on June 21, 1968. Seuss himself died, following several years of illness, in La Jolla, California on September 24, 1991.