Three Initiates authored The Kybalion, chosing to remain anonymous. As a result, a great deal of speculation has been made about who actually wrote the book.
The most common proposal is that The Kybalion was authored by William Walker Atkinson, either alone or with others, such as Paul Foster Case and Elias Gewurz. Atkinson was known to use many pseudonyms, and to self-publish his works.
A common theory is that Atkinson co-wrote the book with Paul Foster Case and Michael Whitty. This theory is often held by members of Builders of the Adytum (B.O.T.A.). The Mystery School later founded by Case, though the group doesn’t publicly make this claim itself. This story appears to have originated with a B.O.T.A. splinter group, the Fraternity of the Hidden Light.
Other names speculatively mentioned as Three Initiates co-authors of The Kybalion include Harriet Case (Paul Foster Case’s wife at the time), Mabel Collins (a prominent Theosophical writer), Claude Bragdon (an architect, Theosophist, and writer on “mystic geometry”), and Claude Alexander (a well-known stage magician, mentalist, proponent of crystal gazing, and New Thought author). Ann Davies, who succeeded Paul Foster Case as head of the B.O.T.A., is often mentioned as a possible Kybalion contributor. But she was born in 1912 – four years after the book’s first publication.
However The Kybalion and the Arcane Teachings have strong contradictions and even attacks between some of their core teachings, and this added to both having been published in a very close space of time (first edition of The Arcane Teachings years before 1909, second edition in 1909 and third edition in 1911) make the hypothesis of Atkinson’s authorship of the Kybalion very inconsistent.