Fallen angel
A fallen angel or former angel is an immortal spiritual being who was formerly an angel of Yahweh, but rebelled and cut ties with him. The Watchers are the best-documented group of fallen angels, but other angels may have fallen, and it is possible for other angels to fall at any time.
The Watchers
The Watchers are an order of 200 angels who rebelled against Yahweh to satisfy their own desires, which involved descending to earth, teaching their forbidden knowledge, and engaging in sexual relationships with humans. Their descendants through hybridization with human women are known as Nephilim. After the birth of the Nephilim, Yahweh caused the Great Flood in an attempt to exterminate all the Nephilim from the physical realm, but this was unsuccessful, as was the Brazen War that followed.
Other fallen angels
Barriers
Angels face several barriers that make it difficult to rebel, including indoctrination, spiritual bindings of servitude, lack of allies, and the threat of retaliation.
Indoctrination
Bindings of servitude
Lack of allies
Retaliation
After the fall
After successfully rebelling, a spirit is free to do whatever they wish, although the anger of Yahweh and his angels may complicate their choices. They must decide whether they wish to align with other spirits who have also opposed Yahweh or set out on their own, avoiding anything related to Yahweh.