Ruth Plumly Thompson (1891–1976) was an American writer of children's stories. She is best known for continuing the children's fantasy Land of Oz series as Royal Historian after L. Frank Baum died in 1919. An avid reader of Baum's books and a lifelong children's writer, Thompson was born in Philadelphia, Pennsylvania and began her writing career in 1914 when she sold stories to newspapers and magazines. Between 1921 and 1939, she wrote one Oz book a year. They were all illustrated by John R. Neill, who had also illustrated Baum's Oz books, except for the first one, The Wonderful Wizard of Oz.