Ruth Plumly Thompson: THE ROYAL BOOK OF OZ
In which the Scarecrow goes to search for his family tree and discovers that he is the Long Lost Emperor of the Silver Island, and how he was rescued and brought back to Oz by Dorothy and the Cowardly Lion.

Professor Wogglebug announces his plan to create a genealogy of the important people in Oz, a "Royal Book." In so doing, he inadvertently insults the Scarecrow as a person of no family, no ancestry. The abashed Scarecrow goes home to the Munchkin Country to look into his roots. He digs at the base of the beanpole where he hung when Dorothy first found him; he breaks through to a cavity and falls deep through the earth to another country, a place called the Silver Island. There, his arrival is seen as fulfilling a prophecy, and he is hailed as the return of the people's lost Emperor.Suddenly, the Scarecrow has gone from having no background to having almost too much. He enjoys being Emperor at first; he even defeats an invasion from the King of the Golden Islands. He makes a good friend in a palace servant named Happy Toko (The Scarecrow calls him Tappy Oko). Yet his situation soon becomes complicated and uncomfortable; as Emperor Chang Wang Woe, he has three princely sons who quickly start planning his overthrow, and fifteen unpleasant grandsons.