The Spalding–Rigdon theory of Book of Mormon authorship is the theory that the Book of Mormon was plagiarized in part from an unpublished manuscript written by Solomon Spalding. The theory first appeared in print in the book Mormonism Unvailed [sic], published in 1834 by E. D. Howe. The theory is that a Spalding manuscript was stolen by Sidney Rigdon, who used it in collusion with Joseph Smith and Oliver Cowdery to produce the Book of Mormon. Although Rigdon claimed that he was converted to the Latter Day Saint movement through reading the Book of Mormon, Howe argued that this story was a later invention to cover the book's true origins.