Lucifer is Satan's real name, and Isaiah 14:12 records his fall from heaven.

The Hebrew word in Isaiah 14:12 is hêlēl ben-šaḥar, "shining one, son of the dawn": a description of the morning star, Venus, and it occurs exactly once in the whole Hebrew Bible. Isaiah 14:4 tells you what you're reading before the famous line even arrives: this is a mašal, a taunt-song, "against the king of Babylon." Verse 16 confirms who's being mocked: onlookers stare at the fallen figure and ask, "Is this the man who made the earth tremble?" A human king, in the same breath as the line people now read as Satan's biography.

The word "Lucifer" itself has a plain paper trail. The Septuagint rendered hêlēl as heōsphoros, "dawn-bringer": still just a description. Jerome's Vulgate (c. 400) translated it as lucifer, the everyday Latin word for Venus that Roman poets had used for centuries: he wasn't unmasking the devil, he was doing ordinary translation work. Wycliffe and the Geneva Bible carried that Latin word straight into English instead of translating it back to "morning star," and the KJV kept it. A lowercase Latin common noun quietly became an uppercase English name, and demonology got built on top of a translator's word choice.

Satan being real and having fallen isn't in question here: Luke 10:18 and Revelation say plainly that he did, and that's established elsewhere in Scripture. This specific verse, in its own context, simply isn't the place that happens. Isaiah is doing something more interesting than people give it credit for: he's borrowing language from a live ancient Near Eastern myth about a lesser god (Athtar) trying and failing to take a throne, and aiming that whole mythic shape at a flesh-and-blood Babylonian tyrant. That's polemic, not biography.