Question: Who is the author of the book that has a musical adaption in which "Over the Rainbow" series in the United Kingdom was auditioning aspiring musical theatre performers for a role?
Sentence (from "The Wizard of Oz (1939 film)"): Widely considered to be one of the greatest films in American history, it is the best-known and most commercially successful adaptation of L. Frank Baum's 1900 children's book, "The Wonderful Wizard of Oz."
Relevant evidence: Yes