The 500 Hats of Bartholomew Cubbins is a children's book, written and illustrated by Theodor Geisel under the pen name Dr. Seuss and published by Vanguard Press in 1938. Unlike the majority of Geisel's books, it is written in prose rather than rhyming and metered verse. Geisel, who was a collector of hats, got the idea for the story when he was on a commuter train from New York to New England, while sitting behind a businessman wearing a hat. The businessman was so stiff and formal that Geisel idly wondered what would happen if he took the man's hat and threw it out the window, and he artistically concluded that the man would "simply grow a new one". The characters of Bartholomew and King Derwin returned a decade later in Bartholomew and the Oobleck. Source: Wikipedia (en)