Here is an unembellished summary of the available biblical data:
ӢJesus and John inform us that Satan was evil "from the beginning" (John 8:44/1 John 3:8)
ӢProverbs states that God made everything for Himself...even the wicked for the day of doom (16:4)
ӢThese verses may or may not be addressing the origin of Satan, but if they are, they suggest that God may have created Satan as a divinely-appointed "tester" (the literal meaning of "tempter"), to test His people's loyalty (as He tested Israel with false prophets--Deut.13:1-4).
ӢThough scripture affirms that some angels have fallen (2 Pet.2:4/Jude 6), no scripture anywhere ever states that Satan is or was himself an angel.
ӢIn the poetic language of Ezekiel (which never mentions Satan), the king of Tyre is said to have been a cherub in the garden of Eden (28:13-14). But later, in the poetic language of the same prophet, the Assyrian is said to have been a tree in the garden of Eden (31:3, 9)! Why should one passage be taken more literally than the other?
ӢA few verses earlier than the disputed Ezekiel passage (v.2), the ruler of Tyre is specifically said to be a "man" (not an angel). The statements that the king of Tyre is "full of wisdom," "perfect in beauty" and "perfect in all thy ways" are clear hyperboles, which were used earlier in the book about the city of Tyre itself (27:3, 28:3). This "king of Tyre" was corrupted by "trading" or "merchandise" (v.16), a distinctive of the city of Tyre, but hardly fitting any scenario of the activities of an un-fallen angel in heaven.
ӢLikewise, "Lucifer" (Isaiah 14:12) is clearly identified as the "king of Babylon" (Isa.14:4) and as a "man" (v.16). The lofty aspirations of "Lucifer" are exactly those of the builders of the Tower of Babel (the origins of Babylon). Lucifer is nowhere identified with Satan in the Bible.
ӢThe fact that Satan was seen by Christ falling "like lightning from heaven" (Luke 10:18) does not tell us anything about Satan's origin. Jesus did not state a timeframe for what He saw, and might well have been seeing prophetically the downfall of Satan which He later describes in John 12:31, and which John describes in Revelation 12:9---both of which seemingly were fulfilled at the cross (cf. Col.2:15/Heb.2:14).
ӢNone can doubt the devil's ability to "be transformed into an angel of light" (2 Cor.11:14), but this does not tell us any more about his actual nature than we can learn about the true character of his ministers from the fact that they "are transformed into ministers of righteousness" (v.15).