The origin is of Hebrew / Judaism mysticism. Some suppose it to be from the Midrash and Talmud oral traditions passed down from the 3rd - 1st century BC, and then later picked up and reprinted as the Book of Enoch.
From Chabad.org, "Nephilim: Fallen Angels, Giants, or Men?"
"The Midrash3 relates that when the generation of the Flood went astray, G‑d began to regret having created man. Then two angels, Shamchazai and Azael,4 came before G‑d and said, “Did we not warn You before You created man, saying, ‘What is man, that You should be mindful of him?’”5 G‑d replied: “Then what shall become of the world?” “We will suffice instead,” they replied. G‑d answered, “I know that would you live on that world, the evil inclination would rule you just as much as it controls man, but you would be even worse.” But the angels persisted, saying: “Let us descend to the world of men, and we will show You how we will sanctify your name.” And G‑d said: “Go down and dwell among them.”
Sure enough, as soon as the angels descended, their evil inclination overpowered them.6 When they saw the beautiful “daughters of man,”7 they became corrupted and sinned with them. They and their descendants are the nephilim, the giants and mighty ones referred to later on in the narrative.
This story is often seen as support for the notion of “fallen angels.” But a careful reading reveals that this is not the case. G‑d sent them down knowing full well—and indeed expecting—that they would end up sinning." (1)
Excerpt from the introduction of Annette Yoshiko Reed's book, "Fallen Angels and the History of Judaism and Christianity, The Reception of Enochic Literature", 2005:
"The brevity of the biblical comments [about Enoch] stands in stark contrast with the wealth of traditions about Enoch in Judaism and Christianity. As early as the Second
Temple period (536 bce to 70 ce), Enoch attracts intensive interest within Judaism. He becomes a scribe, sage, and even scientist. As visionary, he is taken up to heaven and travels with angels to the ends of earth. As witness and prophet, he exhorts against sin, predicts Israel’s history, and even intercedes for wicked angels.Moreover, books begin to circulate under his name, purporting to record the visions and teachings that the antediluvian patriarch passed on to his progeny and bequeathed to the righteous of future generations." (2)
Further, on p. 3 of her introduction:
"Thanks largely to the pioneering research of R. H. Charles (1855–1931), it was established that 1 Enoch is a collection of at least five separate writings and that Syncellus’ quotations derive from the first one (thus dubbed the Book of the Watchers). Speculations about the date, provenance, and original language of these books varied until the discovery of Aramaic fragments of 1 Enoch among the Dead Sea Scrolls and their publication by J. T. Milik from 1951 to 1976.13 The distribution of material in the eleven fragments confirmed Charles’ theory that 1 Enoch is a collection of originally distinct documents. In addition, the paleographical evidence of the earliest fragments suggested that two of these documents, the Astronomical Book (1 En. 72–82) and the Book of the Watchers (1 En. 1 –36), date from the third century bce, making them our oldest known apocalypses and among our most ancient nonbiblical examples of Jewish literature.
The recognition of the antiquity of the Astronomical Book and the Book of the Watchers has revolutionized scholarship on the apocalyptic literature. Although the Astronomical Book may be older, the Book of the Watchers has proved most helpful in illuminating the emergence and development of the genre. Scholars who focus on formal literary features have studied its descriptions of Enoch’s ascent to heaven and his tours of heaven and earth, whereas those who seek to characterize an apocalyptic ideology have pointed to its interest in the Problem of Evil." Source: Ibid
These writings are recognized by scholars to be pseudepigrapha, the definition of which is: "1. Spurious writings, especially writings falsely attributed to biblical characters or times. 2. A body of texts written between 200 bc and ad 200 and spuriously ascribed to various prophets and kings of the Hebrew Scriptures." (3) For instance, if I wrote a book and named it the Book of Adam, it would be pseudigrapha, falsely attributed to Adam, when I was the author.
This is the origin of the so-called Book of Enoch so many are thrilled by today. That a particular Ethiopian copy was "found" in the School of Oriental and Asian Studies (SOAS) library in London, and reprinted by the Oxford University Press is highly suspicious by those who recognize the political agenda of that university with its Rhodes Scholarship funded by the Rothschilds. (4) (5)
The Bible does not say any of this. It was spun from the imaginations of men. When we stay only with what the Bible does say we find that these English translations of the word "angel" is a transliteration, and not a translation. The word "angel" is from the Gr. "angelos" and just means messenger. A messenger is anyone that carries the word of another, and in the scriptures they were messengers of God's word to the people.
Sometimes these messengers were of heavenly origin such as Gabriel and the "angel" of the Lord - messenger of the Lord. The definition also includes the prophets who certainly carried God's word to the people, as well as John the Immerser, Christ himself, the disciples and the apostles. (See also Mal. 3:2) (See also my answer to a previous question on this site regarding the use of angel and messenger here).
The messengers that are described as of greater strength are those messengers (angels) that are from heaven above.
"Whereas angels, which are greater in power and might, bring not railing accusation against them before the Lord." (2 Pet. 2:11, KJV)
One might notice that this distinction in 2 Pet. 2:11 sets apart the angels which are greater in strength from those "angels" in the previous vs. 4 of this same chapter. When some careful analysis is applied, we can see that the original context of this chapter is about the false prophets and teachers - in other words, MEN; and that vs 4 is included among the judgments listed in vs. 5 - 10 which are speaking of MEN.
People are being wrongly influenced by mystical kabbalistic beliefs that originated within 3rd - 1st century BC writings, and are not based in scripture. Those "fallen messengers" were men who failed to abide by God's instructions and were punished just as those men of Noah's day, and those of Sodom and Gomorrah.
Romans 8:14 defines the phrase "sons of God" in the English:
"For as many as are led by the Spirit of God, they are the sons of God." (KJV)
This is God's definition - those led by His spirit are His sons. The Levitical priests were called "gods" as they were His teachers, messengers, and leaders for the people - representing Him before the people.
"I have said, Ye are gods; and all of you are children of the most High." (Psa. 82:6, KJV)
So when Gen. 6:2, 4 are translated as "sons of God" it must abide by God's own word, His definition as His children following after His Spirit, and it is from the preceding chapter 5 which listed out the lineage of those who did follow after God.
Translate the word "angel" in 2 Pet. 2:4 and Jude 1:6 to "messenger" and then keep it in the definition of those who failed and "fell" away from God's word, those who missed the mark (sinned). They did not keep their jobs - their first estate (office), or position which God assigned them to do. The word "estate" in Jude 1:6 is from Strong's Gr. 746, "arche" and means "beginning, origin". It is used for rulers, and magistrates, and falls under definition 5 of Thayer's Greek Lexicon -
"the first place, principality, rule, magistracy (cf. English 'authorities') (ἄρχω τίνος): Luke 12:11; Luke 20:20; Titus 3:1; office given in charge (Genesis 40:13, 21; 2 Macc. 4:10, etc.), Jude 1:6." (6)
The origin of the false belief of these messengers being from heaven, and falling from heaven is of the imagination of men. When we stay strictly with the Bible, the true use as "messengers" assigned to specific tasks by God becomes clear.
"Bless the Lord, ye his angels, that excel in strength, that do his commandments, hearkening unto the voice of his word." (Psa. 103:20, kJV)
The angels / messengers that excel in strength are the ones who face God every single day, and know Him for the supreme ruler over all. Those heavenly angels / messengers do His will. That means they are not fallen.
Those fallen sons of God in Gen. 6:2, 4 cannot be heavenly messengers as they do the will of the Father, and they cannot be doing the will of the Father, nor following after His spirit and also be "fallen" in nature and fallen after the lusts of earthly men. The English translation of Gen. 6:4 in both the KJV and the NIV as "giants" or "Nephilim" is incorrect. Please read my post "Giants: Nephilim, Zamzummim, Emim..." for more background on this scripture at ShreddingTheVeil
More on the Book of Enoch at my post here, and on the "Sons of God" here and here.
The Bible is the inerrant and inspired word of God. When we stay within His word, and abide by His scriptures we will better understand. When we mix His word with that of the imaginations of men (the Book of Enoch), then we get off track.
Fallen Angels and the History of Judaism and Christianity is available here
Definition of pseudepigrapha here
Cecil Rhodes' Wills and the Rhodes Scholarship for World Governance here
So You Thought Rhodes Scholarships Were Good here
Strong's Gr. 746 "arche" here