Great White Brotherhood
The Great White Brotherhood is a concept, not an organization. It is the reassuring idea that even though the world seems destructive and chaotic, there is a hidden group of Spiritual Adepts, some Spirits, some living today, guiding the world and humanity to progress and Spiritual enlightenment.
The original Rosicrucian movement of Johannes Valentinus Andreae appeared after the Protestant Reformation, and was a new Spiritual and Intellectual voice for freedom from orthodoxy and doctrine. The idea was that Man would think for himself, and discover the Godhead within. Only Ignorance held humanity back, not malevolent occult forces.
It's theory of the secret Brotherhood seems heavily influenced by the Jewish legend of the Tzadiks, 10 Holy Men who travel the world, healing it and the sick for free, disguising themselves in the guise of the country in which they travel, and "traveling men" who can't stay in one place for long as people notice they do not age. One legend has it that because they were thus traveling they did not assemble in time to become the 10 Holy Men Abraham had bargained with God would be at Sodom, and the City (and four others) were destroyed by volcano, with only Lot and (most of) his family saved. But more obviously, of course, it is based on Jesus and His disciples, as the Rose (Grace) blooms upon the Cross (Sacrifice), the formula of the Slain God.
The second of the three Rosicrucian Manifestos is clearly political, and rails against the Pope and the Catholics. The duality of God and the Devil fighting for Souls is downplayed, as the two Christian religions are both theoretically on God's side (even if the Pope is secretly an agent of Satan) in these early documents.
But the Philosopher Louis-Claude de Saint-Martin, Father of the Martinist Order, introduced the concept of an Occult Order that was eternal, manifesting only when necessary to prevent Mankind's destruction. This idea was further developed by his student Joséphin Péladan, who emphasized both the Good Adepts and the....evil, whom he called the Black Brothers to characterize their magical goals and practices. People of African ancestry are rare in the history of Western Occultism and the terms Black and White are not being used as racial descriptions.
The useful concept of Hidden Masters dictating otherworldly secrets was very useful to H.P. Blavatsky, who received her teachings in that fashion, sometimes even having physical letters appear in locked boxes. She was the "voice" and could decide what the words meant, but no one could question her about the original material, as it came from "beyond'. When the Hermetic Brotherhood of Luxor began enticing away her students of Eastern Wisdom with Western Magic, she called them the Black Brothers who opposed the Hidden Masters who were trying to guide Mankind.
H. Spencer Lewis also referred to his branch of the Rosicrucian movement, Ancient Mystical Order Rosae Crucis (AMORC), as a part of the White Brotherhood when taking students to see the pyramids of Egypt. He explained that the roots of AMORC were sown there in the sands of the Nile as part of the Great White Brotherhood, which continues to this day.
When relying on Spirit communications rather than Human teachers, Alice Bailey of the the Lucis Trust and her student Elizabeth Clare Prophet of the "Ascended Masters" and 'Church Universal and Triumphant' movements,relied heavily on this idea, and it's connection to Esoteric Christianity.
Much to their chagrin, Guy Ballard, of the I AM movement next claimed the mantle, explaining that aliens and UFOs were an integral part of the Great White Brotherhood's outreach efforts. Similarly, Dr. M. Doreal claimed their mantle, without offering much about them.
However, Omraam Mikhael Aivanhov actually explored the concept in his teachings and books, making a better argument for the continuation of an occult tradition going back ages, which he attributes to the Great White Brotherhood's philosophy today.
It is often contrasted with the "Black Brothers" used to scare Novices and children, but about whom Kenneth Grant developed an entire mythology relating to the Reverse Side of the Tree of Life, the Qlipoth.
Freemasonry is the closest thing we have documented today with the basic goals and tenets of the Great White Brotherhood.