The Hermetic Order of the Golden Dawn was one of the foremost gathering and training grounds for the Magicians
The has been so much written and available on the web and in books, it seems unnecessary to recapitulate what Google can provide.
For the purposes of this WIKI, here are the major players: The founding documents, Cipher Manuscripts were in code, hand written in Kenneth R. H. Mackenzie's script and was reputed by his widow to have been from a document in the possession of Frederick Hockley. In German before encoding, they may have originated from Johann Friedrich Falk, a German in Britain and member of the Kabbalistic College of London who knew both Hockley and MacKenzie. The contents seem similar to the work of Sigismond Bacstrom and the French Rosicrucians. The rituals may well have been adapted from the Golden and Rosy Cross in Germany, (see Sigmund Richter, Johann Georg Gichtel; Hans Heinrich von Ecker und von Eckihoffem; etc.
Purchased by Masonic scholar Rev. A.F.A. Woodford they were passed to another Freemason William Wynn Westcott, who hired a young, poor scholar at the British Museum Library to translate it(the code appears in the works of Johannes Trithemius ). Samuel Liddell MacGregor Mathers had translated other works for Westcott, and both belonged to the the Ancient and Accepted Scottish Rite of Freemasonry's Societas Rosicruciana in Anglia (SRIA) Masonic Rosicrucian group under the United Grand Lodges of England. Inviting fellow Freemason William Robert Woodman, the Supreme Magus of the the Societas Rosicruciana in Anglia, SRIA (after Brother Robert Wentworth Little passed) to join them, they originated the Hermetic Order of the Golden Dawn.
To... apparently make it more mysterious, Westcott told Mathers he had contacted a member of the Continental Rosicrucians, a German woman named Anna Sprengel rather than admit it's origin from Freemason and respected Occultist Kenneth R. H. Mackenzie, whose widow joined the Order soon after it's formation, possibly as an Honoree, there is no record of any advancement. Alexandrina Mackenzie chose the Motto "Cryptonyma", perhaps as her contribution was the encrypted manuscript. Her husband had been Cryptonymus, so she was safe guarding his legacy. Anna Kingsford may have been the model for "Anna Sprengel", whose magical motto was "Soror Sapiens Dominabitur Astris" , the German adept who supposedly chartered the Golden Dawn for Westcott before dying mysteriously. Anna Kingsford's last published work, 1886, included the motto on the cover of a Valentin Weigel translation, " Sapiens dominabitur Asir" aka the Wise Rule their Stars.
The open sub-group of Freemasons in the SRIA had developed a sub-sub group, "Order of Light" in 1882, followed in 1883 by the Masonic organization called the "Society of Eight" formed to study Alchemy. (The 8 may have been turned on it's side as Infinity); "The Hermetic Order of the Golden Dawn was planned by 1888. Unlike Freemasonry, It was the only organization that was co-ed from the beginning, MacGregor Mathers being a strong supporter of Women's Rights.
While the Societas Rosicruciana in Anglia (SRIA), Madame Blavatsky's Theosophical Society, Rudolf Steiner's Anthroposophical Society, Frederick Holland's Society of Eight and Johann Friedrich Falk's Kabbalistic College of London all held lectures, dinners and discussions about occult subjects, these interests seem mostly intellectual rather than practical. The Hermetic Order of the Golden Dawn introduced practice and ritual to what had been discussion, including exercises to develop occult skills. In this, there was little practical Alchemy, which had been the goal of the Order of the Golden and Rosy Cross in Germany, and a strong focus on Qabalah, which both Mathers and Westcott preferred to practical chemistry experiments.
It grew, it fractured, and spawned many groups from this one seminal gathering of minds at the turn of the last century. See
Resources: http://en.wikipedia.org/wiki/Hermetic_Order_of_the_Golden_Dawn; rather than get a synopsis.
Who were it's TEACHERS: Johannes Trithemius; P. B. Randolph; Sigmund Richter; Francis Barrett; Paracelsus ; Eliphas Levi; Papus; Sigismond Bacstrom; Frederick Holland; Frederick Hockley; Kenneth R. H. Mackenzie; Johann Christoph von Wöllner ; General Johann Rudolf von Bischoffwerder ;Rev. A.F.A. Woodford; William Wynn Westcott; Samuel Liddell MacGregor Mathers; William Robert Woodman; Henri Antoine Jules-Bois; William Alexander Ayton; John Yarker ; Cagliostro; Robert Wentworth Little; Johann Georg Gichtel; Hans Heinrich von Ecker und von Eckihoffem; Johann Friedrich Falk; Maurice Vidal Portman ;
Students: (many became leaders, friends or enemies over time): Florence Farr, Irish revolutionary Maud Gonne, Irish writer W.B. Yeats, Welsh author Arthur Machen, author Evelyn Underhill, Aleister Crowley, the Beast 666 ; Paul Foster Case of B.O.T.A of Builders of the Adytum; Dr. Henry B. Pullen Burry; M.W. Blackden; JW.Brodie-Innes; Dr. Robert Felkin ; Edmund Berridge ; Dr Francis Israel Regardie whose Golden Dawn books passed on this knowledge to a new generation in the 1970s; Allan Bennett who became a Yogi; Horror writer Algernon Blackwood ; Alchemist Frederick Leigh Gardner; Annie Horniman; Arthur Henry Sarsfield Ward AKA Sax Rohmer, creator of Fu Manchu ; Tarot artist Pamela Colman Smith; Bram Stoker, creator of Dracula the Vampire; Arthur Edward Waite A.E. Waite; likely Theodore Moriarty; Cris Monnastre; Chic Cicero, Tabitha Cicero; Max Heindel; R. Swinburne Clymer; Kirk White; Robert Word; Robert Zink;
Preceding organizations: Freemasonry; Ancient and Accepted Scottish Rite of Freemasonry; Knights Templar; York Rite of Freemasonry; "Rite of Memphis and Misraim"; The Gold und Rosenkreuzer Golden and Rosy Cross; Societas Roseau Cruis; Societas Rosicruciana in Anglia (SRIA); : Fiat Lucis; Fratres Lucis; Society of Light; Hermetic Brotherhood of Luxor; Order of Illuminati (revived 1902 with Leopold Engel); New Thought movement; Spiritualism; "Golden and Rosy Cross"; "Fraternity of the Rose Cross" ; Cabalistic Order of the Rosicrucian; quasi-Catholic Mystic Order of the Rose + Cross; Ancient Mystical Order Rosae Crucis (AMORC); Rosicrucian Kabbalistic Order of the Rose-Croix aka Kabbalistic Order of the Rosy Cross; Le Rose + Croix Universitaire; L'Order d'Hermes Trismegistus; F.U.D.O.S.I. (Universal Federation of Initiatic Orders and Societies; Order 'L'ORDRE DE LA ROSE-CROIX CATHOLIQUE EST ESTETHIQUE DU TEMPLE ET DU GRAAL'; "Order of Light" AKA the August Order of Light in England; "Society of Eight"; Brotherhood of Eulis; Martinist Order of Freemasonry; Swedenborg Rite of Freemasonry; Order of the Asiatic Brethren; Order of the African Architects;
Succeeding Organizations: A∴A∴ or Argenteum Astrum (the Silver Star); OTO AKA Ordo Templi Orientis; Alpha et Omega ; The Open Source Order of the Golden Dawn; The Hermetic Order of the Golden Dawn, Inc.; The Rosicrucian Order, AMORC; The Order of the Hermetic Gold and Rose + Cross; The Rosicrucian Fellowship; Fraternitas Rosae Crucis; Eulis's Temple of the Rosy Cross; Fraternitas Rosicruciana Antiqua; Great Enlightened Society of Oculists; The Star Lodge;
At the schism of the Golden Dawn, several different organizations sprung up among it's members, as Occultists followed their interests and friends. Samuel Liddell [[MacGregor Mathers], his wife Moina Mathers and J.W. Brodie-Innes, and Edward Berridge remained one branch, the Alpha et Omega; P.W. (Percy) Bullock; M.W. Blackden, W.B. Yeats and DR. Robert Felkin ran the Isis-Urania temple, then formed the Stella Matutina of which Dion Fortune and Dr. Francis Israel Regardie are the most famous members. Aleister Crowley formed the A.A. and then joined the OTO.
Resources: http://en.wikipedia.org/wiki/Cipher_Manuscripts; The Complete Golden Dawn System of Magic by Dr. Francis Israel Regardie; The Magicians of the Golden Dawn by Ellic Howe; The Alchemist of the Golden Dawn: letters of Revd W.A. Ayton to F.L. Gardner and others 1886-1905 by Ellic Howe; The Golden Dawn: the Inner Teachings by R.G.Torrens; Golden Dawn, Twilight of the Magicians by R.A. Gilbert, The Golden Dawn Companion by R.A. Gilbert; see Mottos here - http://www.hermetics.org/GD-motto.html; http://blogs.telegraph.co.uk/news/dominicselwood/100252072/the-dark-deep-roots-of-britains-fascination-with-witchcraft/?fb :