Lucifer is a Latin word meaning "light bearer" (from lux, lucis, "light", and ferre, "to bear, bring"), a Roman astrological term for the "Morning Star" the planet Venus. The word Lucifer was the translation of the Septuagint Greek heosphoros, ("dawn-bearer"; cf. Greek phosphoros, "light-bearer"; itself the translation of the Hebrew Helel ben Shahar, Son of Dawn), used by Jerome in the Vulgate, having mythologically the same meaning as Prometheus who brought fire to humanity.

Passage 14:12 from the Book of Isaiah (see below) referred to one of the popular honorific titles of a Babylonian king; however, later interpretations of the text, and the influence of embellishments in works such as Dante's Inferno and Milton's Paradise Lost, led to the common interpretation in Christian belief that Lucifer was a poetic appellation of Satan.

Modern and late Medieval Christian thought derived from this interpretation the idea that Lucifer is a fallen angel who is Satan, the embodiment of evil and an enemy of God. In Christian literature and legend, Lucifer is generally considered to have been a prominent archangel in heaven, although Book of Ezekiel 28:14 says: "You were the anointed cherub who covers, And I placed you there." In the fully-developed theme of "The War of Heaven", Lucifer had been motivated by pride to lead a revolution against God. When the rebellion failed, Lucifer was cast out of heaven, along with a third of the heavenly host, and came to reside in the world.