Theodor Geisel, better known as Dr. Seuss, was an American author and illustrator who is best known for writing children's books. Some of his most popular books include The Cat in the Hat, Green Eggs and Ham, and How the Grinch Stole Christmas. His books often used imaginative illustrations and whimsical rhyming language. Many of his books were later adapted into films. Dr. Seuss wrote most of his books using anapestic tetrameter, which gave his stories a rhythmic quality that made them fun for children to read. His unique style helped popularize reading for children and he sold over 600 million copies worldwide.