In 1885, Kellner met the Theosophical and Rosicrucian scholar, Dr. Franz Hartmann (1838 - 1912). He and Hartmann later collaborated on the development of the "ligno-sulphite" inhalation therapy for tuberculosis, which formed the basis of treatment at Hartmann's sanitarium near Saltzburg. During the course of his studies, Kellner believed that he had discovered a "Key" which offered a clear explanation of all the complex symbolism of Freemasonry, and, Kellner believed, opened the mysteries of Nature. Kellner developed a desire to form an Academia Masonica which would enable all Freemasons to become familiar with all existing Masonic degrees and systems.
In 1895, Kellner began to discuss his idea for founding an Academia Masonica with his associate Theodor Reuss (Merlin or Peregrinus, June 28 1855 - 28 October 1923). During these discussions, Kellner decided that the Academia Masonica should be called Ordo Templi Orientis (Oriental Templar Order). The occult inner circle of this Order (O.T.O. proper) would be organized parallel to the highest degrees of the Masonic Rite of Memphis and Mizraim and would teach the esoteric Rosicrucian doctrines of the Hermetic Brotherhood of Light, and Kellner's "Key" to Masonic symbolism. Both men and women would be admitted at all levels to this Order, but possession of the various degrees of Craft and High-Grade Freemasonry would be a prerequisite for admission to the Inner Circle of O.T.O.
Unfortunately, due to the regulations of the established Grand Lodges which governed Regular Masonry, women could not be made Masons and would therefore be excluded by default from membership in Ordo Templi Orientis. This may have been one of the reasons that Kellner and his associates resolved to obtain control over one of the many rites, or systems, of Masonry; to reform the system for the admission of women.
The discussions between Reuss and Kellner did not lead to any positive results at the time, because Reuss was very busy with a revival of the Order of Illuminati along with his associate Leopold Engel (1858-1931) of Dresden. Kellner did not approve of the revived Illuminati Order or of Engel. According to Reuss, upon his final separation with Engel in June 1902, Kellner contacted him and the two agreed to proceed with the establishment of Ordo Templi Orientis by seeking authorizations to work the various rites of high-grade Masonry. Reuss and Kellner together prepared a brief manifesto for their Order in 1903, which was published the next year in The Oriflamme. Kellner died on June 7 1905.