Isa 14:12 is commonly appealed to as a reference to Satan as a fallen angel, but this understanding is first promoted in the deuterocanonical literature, not in the Hebrew Bible. In Job 2:1, dated roughly to the third or fourth century BCE, Satan, here a proper noun associated with a divine being, is grouped with the bĕnê ha’ĕlohîm. He is not a messenger there and is never equated with the mal’ākîm anywhere in the Hebrew Bible. His rebelliousness is comparable to that of the bĕnê ’ĕlohîm in Genesis 6 and to the sons of ’Ilu from the Ugaritic pantheon, although his antagonism is aimed at humanity rather than at his divine superiors, which makes the association with Ugaritic literature strained. In all the literature of the Hebrew Bible, the mal’ākîm are never portrayed as disobedient. As with all Syro-Palestinian messengers, they were strictly obedient. Only in early apocryphal and pseudepigraphical literature do fallen angels begin to emerge as Second Temple texts began to explore Judaism’s theological boundaries. Satan’s existence in the Hebrew Bible represents, in my opinion, a middle ground between the earliest attested Israelite theology and the later literature that relegated him to the realms of the angelic hosts.
In the early theology YHWH is the originator of both good and evil. Whether independently or by analogy with other dualistic religions (like Zoroastrianism), Israel slowly developed an individualized divine antithesis to God, who adopted the title Satan (“Adversary”). In 2 Sam 24:1, YHWH, in his anger, compels David to number Israel and Judah. In the post-exilic 1 Chr 21:1 it is Satan who compels David. This verse provides a Second Temple reinterpretation of the event that ascribes the inspiration to sin to an adversary rather than to YHWH. This adversary could hardly be taxonomically related to God in the Second Temple world, and so was demoted to the realm of the angels. This demotion coincided with the relegation of the “sons of God” to angelic status (see here). In this way, Judaism’s recently developed dualism was reconciled with its developing monotheism and YHWH’s universalism.
 Prior to this the word śāṭān is used as a generic noun rather than a personal name. See Num 22:22; 1 Sam 29:4; 1 Kgs 11:14. See Zech 3:1–2 for another example of Satan as a personal name.
 In the story of Balaam and the angel of YHWH (Num 22:22) the angel is called a śāṭān, but the word is clearly being used in its generic and indefinite sense.
 In 1 Sam 2:6–7, for instance, YHWH kills and makes alive, brings riches and poverty, and exalts and makes low. Again in Isa 45:6–7 YHWH forms light and darkness, and makes peace as well as evil. In 1 Kgs 11:14 it is YHWH who establishes an adversary (sāṭān) against Solomon. As was pointed out long ago by Helmer Ringgren (Israelite Religion [trans. David E. Green; Philadelphia: Fortress Press, 1966], 72–73), much of the opposition to Israel and her heroes was actually inspired by YHWH (see Exod 9:12; 10:1; Judg 9:23; 1 Sam 16:14; 19:9–10; 1 Kgs 22:19–23; Amos 3:6).
 Isa 45:6–7 (a rather late text) may act as a polemic against Zoroastrian dualism, asserting YHWH is the source of everything, both good and evil. This would provide an intermediate reaction to theological dualism that preceded its appropriation and the development of Satan as a fallen angel.
 Shaye J. D. Cohen, From the Maccabees to the Mishna, Second Edition (Louisville, Kent.: Westminster John Knox, 2006), 79–80; 85–86.