Grigori or Watcher Angels: “those who are awake”; “guard”, “watcher” is a term used in connection with biblical angels. Watcher occurs in both plural and singular forms in the Book of Daniel (2nd century BC), where reference is made to their holiness. The apocryphal Books of Enoch (1st and 2nd centuries BC) refer to both good and bad Watchers, with a primary focus on the rebellious ones. Guess which one I’m going to talk about?
In the Book of Enoch, the Watchers are angels dispatched to Earth to watch over the humans. They soon begin to lust for human women and, at the prodding of their leader Samyaza, defect en masse to illicitly instruct humanity and procreate among them. The offspring of these unions are the Nephilim, savage giants who pillage the earth and endanger humanity. Samyaza and his associates further taught their human charges arts and technologies such as weaponry, cosmetics, mirrors, sorcery, and other techniques that would otherwise be discovered gradually over time by humans, not foisted upon them all at once. Eventually God allows a Great Flood (Yes that Flood) to rid the earth of the Nephilim, but first sends Uriel to warn Noah so as not to eradicate the human race. The Watchers are bound “in the valleys of the Earth” until Judgment Day. (Jude verse 6 says that these fallen angels are kept “in everlasting chains under darkness” until Judgement Day.)
The book of Enoch also lists leaders of the 200 fallen angels who married and commenced in unnatural union with human women, and who taught forbidden knowledge. Some are also listed in Book of Raziel (Sefer Raziel HaMalakh), the Zohar, and Jubilees.