Canonical Christian tradition speaks about the Angels of Heaven and the Fallen Angels who battled for Lucifer in the War of Heaven. There is, however, a third group of Angels that are not as well known.
The Grigori (from Greek egrgoroi, "The Watchers") are a group of “fallen” angels, described in both the Old Testament and Biblical Apocrypha, who mated with mortal women, giving rise to a race of hybrids known as the Nephilim, who are described as giants and “heroes of old, the men of renown”. References to angelic Grigori appear in the books of Enoch, Lamentations, Daniel and Jubilees. In Hebrew, they are known as the Irin, or "Watchers”.
In Enoch, the Watchers are angels apparently dispatched to Earth simply to watch over the people and teach law and justice to humankind. Once on earth, they begin to lust for the human women they see, and at the prodding of their leader Samyaza, they defect en masse to marry and live among men. The children produced by these relationships are the Nephilim, savage giants who pillage the earth and endanger humanity. Samyaza, Azazel, and the others become corrupt, and teach their human hosts to make metal weapons, cosmetics, and other necessities of civilization that had been kept secret.
Jubilees tells a similar story to Enoch:
“Against his angels whom he had sent to the earth he [God] was angry enough to uproot them from all their (positions of) authority”
"For it was on account of these three things [fornication, uncleanness, and injustice - see Jubilees 7:20] that the flood was on the earth, since (it was) due to fornication that the Watchers had illicit intercourse - apart from the mandate of their authority - with women. When they married of them whomever they chose they committed the first (acts) of uncleanness. They fathered (as their) sons the Nephilim.
God sends the Great Flood to rid the earth of the Nephilim, but sends Uriel to warn Noah so as not to eradicate the human race. The Grigori are bound in chains and eternal darkness until Judgment Day.
The Book of Jubilees adds further details about the Watchers. While "Watchers" or "Sentinels" are mentioned alongside the "holy ones" in the Book of Daniel, it is doubtful they have any connection to the Grigori. The angels were fairly popular in Jewish folklore, which often describes them as looking like large human beings that never sleep and remain forever silent. While there are good and bad Watchers, most stories revolve around the evil ones that fell from grace when they took "the daughters of man" as their mates.
According to the Book of Enoch, the Grigori numbered a total of 200 but only their leaders are named:
"These are the names of their chiefs: Samyaza, who was their leader, Urakabarameel, Akibeel, Tamiel, Ramuel, Danel, Azkeel, Saraknyal, Asael, Armers, Batraal, Anane, Zavebe, Samsaveel, Ertael, Turel, Yomyael, Azazyel (also known as Azazel). These were the prefects of the two hundred angels, and the remainder were all with them."
~1 Enoch 7:9
Not all religious traditions teach that not all the Grigori were bad. Earlier mystical Hebrew sects organized the Watchers into an Archangel hierarchy. According to this system, the Watchers were ruled over by four great Watchers known as Michael, Gabriel, Raphael, and Auriel. In the Old Testament (Daniel 4: 13 17) there is reference made to the Irin, or Watchers, which appear to be an order of angels. In early Hebrew lore, the Irin were a high order of angels that sat on the supreme Judgment Council of the Heavenly Court.
Other traditions link the Grigori to the Titans of Greek mythology. The Titans were also of divine lineage and some, like Prometheus, taught mankind and raised them from basic hunter/gathers to the founders of civilizations.
A list of named Grigori and what they taught mankind can be found in The Angelus: A Compendium of Angelical Rituals and Attunements . For more information about the free eBook which is available to all Members, visit the Member Area above.
The word "egregore" (also "grigori") is a transliteration of the Greek word, egregoroi, meaning "watchers". This word appears in the Septuagint translation of the Book of Lamentations, as well as the Book of Jubilees and the Book of Enoch.  The term “fallen” refers to a fall from God’s Grace as opposed to those who went to war against him.  Genesis 6:4  Daniel 4  Jubilee 4:15-16  Jude 1:6