Unearthly entity first contacted by (or contactor of) Aleister Crowley in Cairo, 1901 who dictated the Book of the Law to him.
From The Equinox of the Gods:
I went into the “temple” a minute early, so as to shut the door and sit down on the stroke of Noon.
On my table were my pen–a Swan Fountain–and supplies of Quarto typewriting paper, 8″ x I0″.
I never looked round in the room at any time.
The Voice of Aiwass came apparently from over my left shoulder, from the furthest corner of the room.
…
The voice was of deep timbre, musical and expressive, its tones solemn, voluptuous, tender, fierce or aught else as suited the moods of the message. Not bass –perhaps a rich tenor or baritone.The English was free of either native or foreign accent, perfectly pure of local or caste mannerisms, thus startling and even uncanny at first hearing.
I had a strong impression that the speaker was actually in the corner where he seemed to be, in a body of “fine matter,” transparent as a veil of gauze, or a cloud of incense-smoke. He seemed to be a tall, dark man in his thirties, well-knit, active and strong, with the face of a savage king, and eyes veiled lest their gaze should destroy what they saw. The dress was not Arab; it suggested Assyria or Persia, but very vaguely. I took little note of it, for to me at that time Aiwass and an “angel” such as I had often seen in visions, a being purely astral.
I now incline to believe that Aiwass is not only the God or Demon or Devil once held holy in Sumer, and mine own Guradian Angel, but also a man as I am, insofar as He uses a human body to make His magical link with Mankind, whom He loves, and that He is thus and Ipsissimus, the Head of the A∴A∴ Even I can do, in a much feebler way, this Work of being a God and a Beast, &c., &c., all at the same time, with equal fullness of life.
Based on the work of Kenneth Grant, some have suggested the “personal guardian angel” AIWASS was the same entity as the penis-headed gray alien “Lam.” But that is just a bunch of speculative bullshit.