The collective of magicians known as the Black Brothers mentioned in Aleister Crowley's Liber ABA (Book 4).

Their stronghold is a Tower built upon the edge of the Abyss. These adepts have refused to let go of their attainments (and their egos) and cross the abyss into the City of the Pyramids. Eventually they will be worn away by the inertia of the Universe. Theirs is but one byway on the journey of the Magnum Opus, their stubborness bars them from further attainment as well as the Secret Word of the Aeon.

Further accounts of them may be found in "One Star in Sight".