Isaiah 14:12
12How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! 13For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:
14I will ascend above the heights of the clouds; I will be like the most High.
15Yet thou shalt be brought down to hell, to the sides of the pit.
The passage actually predicts the fall of Babylon. The word translated as "Lucifer" is the Hebrew "helel", referring to the planet Venus when it appears as the morning star, which is known in Latin as "Luciferus, or "light bringer". The writer of Isaiah was comparing the might of the Babylonia Empire to the morning star, which shines brightly until its light is overwhelmed by that of the Sun, which would represent Persia. Most modern translations use "morning star", instead of Lucifer.
The concept of a conflict in heaven exist in many mythologies with gods fighting among themselves and the losers getting cast out to some sort of eternal confinement or punishment (the Titans, Loki). The early Christians merged Helel/Luciferus with the Hebrew Satan and began creating the myth of a fallen angel, which grew in details during the Middle Ages, ending in Milton's great epic.
As for angels, in the Old Testament, only some of them are remotely human, although some, like the one's that visited Lot, can look human.
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