Holy Guardian Angel

The term Holy Guardian Angel originates in the Catholic Church where a morning prayer is recited which reads, "Holy Guardian Angel whom God has appointed to be my guardian, direct and govern me govern me during this day/ Amen". The idea of a Holy Guardian Angel is central to the book, "The Book of the Sacred Magic of Abra Melin the Mage", Abraham of Worms, a German Cabalist who wrote the book on ceremonial magick during the 15th century which was later translated by Samuel Liddell MacGregor Mathers, the founder of the Hermetic Order of the Golden Dawn. He elaborated on this earlier work, giving it extensive magical notes, but the original concept goes back to the Zoroastrian Arda Fravaš ('Holy Guardian Angels'). In Mathers' publication of The Book of the Sacred Magic of Abramelin the Mage, he writes:

Later, author and occultist Aleister Crowley popularized the term within his religious and philosophical system of Thelema.

Within the system of the magical Order A∴A∴ founded by Aleister Crowley, one of the two most important goals is to consciously connect with one’s Holy Guardian Angel, representative of one's truest divine nature: a process termed “Knowledge and Conversation.”

In some branches of occultism, the term is so widely known that HGA has become a common abbreviation even in non-English-speaking countries. Crowley seems to consider it equivalent to the Genius of the Hermetic Order of the Golden Dawn, the Augoeides of Iamblichus, the Atman of Hinduism, and the Daemon of the ancient Greeks. He borrowed the term from the Grimoire "The Sacred Magic of Abramelin the Mage".

...
Wikipedia