A Watcher is a type of biblical angel. The word occurs in both plural and singular forms in the Book of Daniel, where reference is made to the holiness of the beings. The apocryphal Books of Enoch refer to both good and bad Watchers, with a primary focus on the rebellious ones.
Watching angel on the spire of St Michael's church, Clifton Hampden, Oxfordshire, England
The Book of Enoch is an ancient Hebrew apocalyptic religious text, ascribed by tradition to the patriarch Enoch who was the father of Methuselah and the great-grandfather of Noah. The Book of Enoch contains unique material on the origins of demons and Nephilim, why some angels fell from heaven, an explanation of why the Genesis flood was morally necessary, and a prophetic exposition of the thousand-year reign of the Messiah. Three books are traditionally attributed to Enoch, including the distinct works 2 Enoch and 3 Enoch.
Chester Beatty XII, Greek manuscript of the Book of Enoch, 4th century
4th century AD manuscript, with the end of 'The Epistle of Enoch' and the beginning of the Passion homily of 'Melito'; note the large text reading ΕΠΙΣΤΟΛΗ ΕΝΩΧ (EPISTOLĒ ENOCH)