Theodor Seuss Geisel, the children’s author who wrote under the pen name Dr. Seuss, will have his newest book published posthumously Wednesday. Widow Audrey Geisel was going through boxes of his old work in 2013 when she discovered the papers that eventually would become his 47th book, What Pet Should I Get? Geisel passed away in 1991 at age 87; his career spanned decades with his first success coming with 1957's The Cat in the Hat. The first printing of What Pet Should I Get? expected to run one million copies.