In his long life Geisel wrote more than 60 books. He started to write his stories because when he opened his window he heard the animals from the nearby zoo. Geisel wrote most of his books using the name Dr. Seuss. However, he also wrote 13 books using the name Theo. LeSieg. He also wrote one book using the name Rosetta Stone"—"the same name as the Rosetta Stone. Many people know and like Theodor Seuss Geisel's work as a children's author. His books are known for catchy phrases. His books have sold over 222 million copies and been translated into more than 15 languages. After his death in 1991, several books have been published based on his sketches and notes; these include "Hooray for Diffendoofer Day!" and "Daisy-Head Mayzie". Though they were all published under the name Dr. Seuss, only "My Many Colored Days", originally written in 1973, was entirely by Geisel. Before his death, he sold 200 million copies of his books. One museum in Springfield, Massachusetts is completely about Geisel and his books. 