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!. 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.