Margaret Landon became interested in the story of Anna Leonowens, a governess in the court of King Mongkut, while living in Thailand. Leonowens published two books about her experiences: The English Governess at the Siamese Court and The Romance of the Harem. Landon published several articles about Leonowens, and in 1942 completed Anna and the King of Siam, which sold 790,000 copies in the United States and the United Kingdom alone. I haven't read the novel yet, but I'll add my thoughts here when I do! For more about the real Anna, check out this site.