LUCIFER ("lightbearer"), the name given to the "morning star," i.e. the planet Venus when it appears above the E. horizon before sunrise, and sometimes also to the " evening star," i.e. the same planet in the W. sky after sundown, more usually called Hesperus (q.v.). The term " day star " (so rendered in the Revised Version) was used poetically by Isaiah for the king of Babylon: " How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations " (Is. xiv. 12, Authorized Version). The words ascribed to Christ in Luke x. 18: "I beheld Satan as lightning fall from heaven " (cf. Rev. ix. i), were interpreted by the Christian Fathers as referring to the passage in Isaiah; whence, in Christian theology, Lucifer came to be regarded as the name of Satan before his fall. This idea finds its most magnificent literary expression in Milton's Paradise Lost. In this sense the name is most commonly associated with the familiar phrase " as proud as Lucifer."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)