According to Christian tradition, Satan has a backstory: The devil was once the most beautiful angel in heaven but this angelic being, then called Lucifer, rebelled against God and was cast down to hell. In part, this tradition comes from a particular interpretation of Isaiah 14:12-15. The text describes someone who, in Isaiah’s original Hebrew, is called Helel ben Shachar (הילל בן שׁחר)--variously translated as “Day/Morning Star, son of Dawn/Morning” (14:12). In the Latin Vulgate, the Hebrew “Helel” becomes Lucifer. Yet, while Isaiah taunts someone who equates himself with God and suffers the consequences, the prophet does not disclose the origin of evil. Instead, Isaiah 14 refers to the king of Babylon, and “Satan” appears nowhere in the passage. Thus, if we ground our theological understanding on Scripture alone, then we have no reason to posit an angelic prehistory for Satan based on Isaiah.
Isaiah addresses Helel ben Shachar, saying, “How you are fallen from heaven.... You said in your heart, ‘I will ascend to heaven; above the stars of God I will set my throne on high.... I will make myself like the Most High’” (14:12-14). Responding to Helel’s hubris, Isaiah tells him, “You are brought down to Sheol, to the far reaches of the pit” (14:15). Taken out of context, Isaiah’s taunt can certainly be made to refer to an angel who rebelled in heaven and ended up in hell; hence, the start of Satan’s antipathy toward God and humanity. Yet, immediately before the above verses, Isaiah tells Israel that after their exile ends they will “take up this taunt against the king of Babylon (מלך בבל; melekh bavel)” (14:4). The prophet addresses an earthly king, not a rogue angel in heaven.
Those who see Shachar as Satan might object that the text should be understood in both ways: while Isaiah does address a human king, there is a spiritual reality beyond the earthly focus. However, this interpretive assumption can only be speculative since the Bible itself provides no textual data that would lead us to associate the story with Satan. Interestingly, Isaiah 14:12-15 may be an Israelite reworking of an Ugaritic tale called the Baal-Athtar myth, in which a divine underling is punished for attempting to dethrone the reigning Canaanite deity. While parallels exist between this ancient narrative and Isaiah, neither text mentions "Satan" (שׂטן). More, while Isaiah may sound something like an Ancient Near Eastern myth about polytheistic conflict, the Hebrew prophet repurposes the story to speak of Babylon’s monarch; that is, Isaiah humanizes the story and applies it to a Gentile king.
Finally, Isaiah’s text does not affirm the traditional story of Satan’s fall from heaven. According to popular tradition, Lucifer begins in heaven and is cast down; in Isaiah, “Lucifer” says, “I will ascend [to] heaven (השׁמים אעלה; hashamayim e’eleh)" (14:13). In Scripture, the arrogant individual begins on earth—fitting for an earthly king—and resolves to work his own way to God in heaven. More, Isaiah’s king is “brought down to Sheol (שׁאול)” (14:15)—not to “hell” (גהינם; gehinnom)—which means he dies: “Your pomp has brought you down to Sheol... the maggot is laid as a bed beneath you, and the worm is your covering” (14:11). The “maggot” (רמה; rimah) and “worm” (תולעה; toleah) are biblical metaphors for death and decay (e.g., Isa 41:14; Job 17:14; 21:26; 24:20; cf. Isa 66:24). Isaiah chastises a mortal king whose fate is in the ground, not a supernatural usurper who now reigns unrepentantly in hell. Though the Bible mentions “Satan” outside of Isaiah 14, it does not provide narrative insight into his origins; Scripture is concerned, not with Satan’s past, but with the present and future sovereignty of God.