Many people believe that Satan used to be Lucifer, one of the highest archangels in heaven. This isn't supported by Scripture as we'll see by the following evidences. Lucifer was actually a reference to the king of Babylon in Isaiah.
This is from a note in the Chronological study Bible called "a failed assault on heaven."
"The prophet Isaiah uses mythological language in a proverb mocking the king of Babylon (Is. 14:4, 22). His references to the day star, the ascent into heaven, the mount of the congregation, and to Sheol would all have been familiar to his readers from the myths of the ancient near east. The name 'Lucifer' is a latin translation of the Hebrew word helel meaning 'shining one.' Lucifer refers to the day star, Venus, and the prophet further identifies him as 'the son of the morning' (14:12). Similar language appears appears with the Ugaritic deities Shahar and Shalim. Shahar was the god of dawn or morning; Shalim, the god of dusk or evening. In another Ugaritic text, Shahar (morning) appears together with Athtar, the star deity who is also identified with Venus.So the ancient myths possibly had made Isaiah's readers familiar with the day star whose father was the god of the morning. Isaiah's taunt of the day star for wanting to ascend into heaven (14:13) may reflect the Ugaritic myth of Athtar, the Venus star deity who is also identified with Venus. Athtar attempts to ascend to the throne of Baal, but is not able and is forced to return to his own, lower position of the pantheon. Athtar was not storming heaven, only sitting on the vacated throne of Baal. He excuses himself from the position upon realizing that he is too small. Nevertheless, a day star ascending to heaven was known in Canaanite myth. In Isaiah's proverb, the day star desires to sit on 'the mount of congregation' located 'on the farthest sides of the north (14:13).' Similarly, Canaanite myths spoke of the mountain home of Baal on Saphon (the Hebrew word translated 'north') and also of a mount of assembly. In Isaiah's proverb, the day star fails to ascend to heaven and is brought down to Sheol, the netherworld also called the pit (14:15.) Similarly, in ancient Near Eastern mythology gods could die and be sent to Mot's netherworld. The reason that Baal's throne was vacant in the Ugaritic myth was that Mot had vanquished Baal and taken him to the realm of the dead."
This is from another note.
"The planet Venus was an important subject for ancient mythology. It is bright when it rises, but when the sun comes up, Venus becomes invisible like any other star. The prophet mocks the king of Babylon, calling him "Lucifer" (Is. 14:12), a translation of the Hebrew word for the day star Venus. The king was trying to rival the sun, and the prophet rebuked him in these terms."
Many people interpret the "heaven" and "sacred mountain" in Isaiah to be referring to the abode of YHWH. Nevertheless, it actually refers to the dwelling place of false idols. This note is taken from the Archaeological study Bible.
"The sacred mountain is mount Zaphon which is northeast of Ugarit in Syria. Much like Mount Olympus for the Greeks, the Canaanites considered this holy mountain to be the dwelling and meeting place of the gods."
It's interesting to note there's no concept of Satan originally being an angel in ancient Jewish theology.
With all of these evidences, it's clear that the tale of Satan originally being an angel is false doctrine.
This is from a note in the Chronological study Bible called "a failed assault on heaven."
"The prophet Isaiah uses mythological language in a proverb mocking the king of Babylon (Is. 14:4, 22). His references to the day star, the ascent into heaven, the mount of the congregation, and to Sheol would all have been familiar to his readers from the myths of the ancient near east. The name 'Lucifer' is a latin translation of the Hebrew word helel meaning 'shining one.' Lucifer refers to the day star, Venus, and the prophet further identifies him as 'the son of the morning' (14:12). Similar language appears appears with the Ugaritic deities Shahar and Shalim. Shahar was the god of dawn or morning; Shalim, the god of dusk or evening. In another Ugaritic text, Shahar (morning) appears together with Athtar, the star deity who is also identified with Venus.So the ancient myths possibly had made Isaiah's readers familiar with the day star whose father was the god of the morning. Isaiah's taunt of the day star for wanting to ascend into heaven (14:13) may reflect the Ugaritic myth of Athtar, the Venus star deity who is also identified with Venus. Athtar attempts to ascend to the throne of Baal, but is not able and is forced to return to his own, lower position of the pantheon. Athtar was not storming heaven, only sitting on the vacated throne of Baal. He excuses himself from the position upon realizing that he is too small. Nevertheless, a day star ascending to heaven was known in Canaanite myth. In Isaiah's proverb, the day star desires to sit on 'the mount of congregation' located 'on the farthest sides of the north (14:13).' Similarly, Canaanite myths spoke of the mountain home of Baal on Saphon (the Hebrew word translated 'north') and also of a mount of assembly. In Isaiah's proverb, the day star fails to ascend to heaven and is brought down to Sheol, the netherworld also called the pit (14:15.) Similarly, in ancient Near Eastern mythology gods could die and be sent to Mot's netherworld. The reason that Baal's throne was vacant in the Ugaritic myth was that Mot had vanquished Baal and taken him to the realm of the dead."
This is from another note.
"The planet Venus was an important subject for ancient mythology. It is bright when it rises, but when the sun comes up, Venus becomes invisible like any other star. The prophet mocks the king of Babylon, calling him "Lucifer" (Is. 14:12), a translation of the Hebrew word for the day star Venus. The king was trying to rival the sun, and the prophet rebuked him in these terms."
Many people interpret the "heaven" and "sacred mountain" in Isaiah to be referring to the abode of YHWH. Nevertheless, it actually refers to the dwelling place of false idols. This note is taken from the Archaeological study Bible.
"The sacred mountain is mount Zaphon which is northeast of Ugarit in Syria. Much like Mount Olympus for the Greeks, the Canaanites considered this holy mountain to be the dwelling and meeting place of the gods."
It's interesting to note there's no concept of Satan originally being an angel in ancient Jewish theology.
With all of these evidences, it's clear that the tale of Satan originally being an angel is false doctrine.