AGLA is a Kabbalistic divine name formed the method of notariqon from the Hebrew sentence Ateh gibor le-olam Adonai, «Mighty are Thou forever, Lord.» It was prevalently used in ceremonial magic during medieval times as AGLA was a word thought to hold power over demons. In magic of the Golden Dawn the name governs the passive aspect of the spirit, and it is also used in the northern quarter in the Lesser Ritual of the Pentagram.
The word also was found in books of magic, notably the Enchiridion of Pope Leo. A.G.H.
Source:
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul, MN, Llewellyn Worldwide. p. 8