DEO is the seventh of the thirty Aethyrs, or Airs, of the Enochian system, the thirty spiritual regions delivered to the mathematician John Dee and the scryer Edward Kelley in 1584, and named in the record Dee compiled from those sessions. Its three-letter name, DEO, was received letter by letter through Kelley's scrying.
Place in the system
Each Aethyr is said to contain three Governors among whom the ninety-one Parts of the Earth are divided.
The thirty Aethyrs are the raw gift of the Dee-Kelley sessions; the elaborate visionary content attached to them in modern practice belongs to a later layer, above all Aleister Crowley's The Vision and the Voice, his record of scrying all thirty Aethyrs in 1900 and 1909. The Aethyr is described here as an element of that documented historical tradition, studied as such, its entities not reified.
The three Governors
DEO's Parts belong to Opmacas, ruling Getulia, the interior of North Africa south of the settled coast, under King Zarnaah of the tribe of Manasseh; to Genadol, ruling Arabia broadly, under King Hononol of the tribe of Judah; and to Aspiaon, ruling a Part called Phalagon, a name with no known geographical referent, under King Zinggen of the tribe of Zebulun. Crowley worked this and the other Aethyrs in 1900 in Mexico and completed the set in 1909 in Algeria, but his visions carry throughout the Kabbalistic scheme he brought from the Golden Dawn, which makes them evidence about Crowley's own practice rather than about what Dee received in 1584.