Why is the writer called Dr. Seuss if that is not his real name?

Many authors write under "pen names" (pseudonyms) for various reasons*. In the case of Theodor Seuss Geisel, Dr. Seussdeveloped as a nickname he used while writing for his college newspaper. He also wrote stories using the names "Theo Le Sieg" (his last name backward) and "Rosetta Stone." But he is promarily known for his perenially popular series of Children's Books.

(*Another famous US author, Samuel Clemens, used the pen name Mark Twain.)