The bible teaches that Satan took 1/3 of the angels and rebelled from God, these are called the Fallen Angels.

From Genesis, Chapter 6:

“There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare [children] to them, the same [became] mighty men which [were] of old, men of renown.”

That they fell, we can read about in other  places in the Bible AND theological letters/books:

Book of Job, 1:6:

{1:6} Now there was a day when the sons of God (Angels) came to present themselves before the LORD, and Satan came also among them. {1:7} And the LORD said unto Satan, Whence comest thou? Then Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it.

2nd Peter, Chapter 2:

{2:4} For if God spared not the angels that sinned, but cast [them] down to hell, and delivered[them] into chains of darkness, to be reserved unto judgment;

Jude Chapter 1:

{1:6} And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.

{1:9} Yet Michael the archangel, when contending with the devil he disputed about the body of Moses, durst not bring against him a railing accusation, but said, The Lord rebuke thee.

{1:14} And Enoch also, the seventh from Adam, prophesied of  these, saying, Behold, the Lord cometh with ten thousands of his saints, {1:15} To execute judgment upon all, and to convince all that are ungodly among them of all their ungodly deeds which they have ungodly committed, and of all their hard [speeches] which ungodly sinners have spoken against him.

Pauls letter to the Corinthians, Chapter 11:10:

“For this cause ought the woman to have power on [her] head because of the angels.”

Here he alludes to the angel’s who fell because of the beauty of women.

Book of Revelation, Chapter 12:

{12:1} And there appeared a great wonder in heaven; a woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars: {12:2} And she being with child cried, travailing in birth, and pained to be delivered. {12:3} And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads. {12:4} And his tail drew the third part of the stars of heaven, and did cast them to the earth: and the dragon stood before the woman which was ready to be delivered, for to devour her child as soon as it was born. {12:5} And she brought forth a man child, who was to rule all nations with a rod of iron: and her child was caught up unto God, and [to] his throne. {12:6} And the woman fled into the wilderness, where she hath a place prepared of God, that they should feed her there a thousand two hundred [and] threescore days. {12:7} And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, {12:8} And prevailed not;  neither was their place found any more in heaven. {12:9} And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him. {12:10} And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night. {12:11} And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death. {12:12} Therefore rejoice, [ye] heavens, and ye that dwell in them. Woe to the inhabiters of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time. {12:13} And when the dragon saw that he was cast unto the earth, he persecuted the woman which brought forth the man [child. ]{12:14} And to the woman were given two wings of a great eagle, that she might fly into the wilderness, into her place, where she is nourished for a time, and times, and half a time, from the face of the serpent. {12:15} And the serpent cast out of his mouth water as a flood after the woman, that he might cause her to be carried away of the flood. {12:16} And the earth helped the woman, and the earth opened her mouth, and swallowed up the flood which the dragon cast out of his mouth. {12:17} And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ.

From the Book of Enoch: (Enoch’s book is referenced above, in Jude 1:14)

1It happened after the sons of men had multiplied in those days, that daughters were born to them, elegant and beautiful. 2And when the angels, (3) the sons of heaven, (Watchers) beheld them, they became enamoured of them, saying to each other, Come, let us select for ourselves wives from the progeny of men, and let us beget children.

3Then their leader Samyaza said to them; I fear that you may perhaps be indisposed to the performance of this enterprise; 4And that I alone shall suffer for so grievous a crime. 5But they answered him and said; We all swear; 6And bind ourselves by mutual execrations, that we will not change our intention, but execute our projected undertaking.  7Then they swore all together, and all bound themselves by mutual execrations. Their whole number was two  hundred, who descended upon Ardis, (4) which is the top of mount Armon.

8That mountain therefore was called Armon, because they had sworn upon it, (5) and bound themselves by mutual execrations.

9These are the names of their chiefs: Samyaza, who was their leader,  Urakabarameel, Akibeel, Tamiel, Ramuel, Danel, Azkeel, Saraknyal, Asael, Armers, Batraal, Anane, Zavebe, Samsaveel, Ertael, Turel, Yomyael, Arazyal. These were the prefects of the two hundred angels, and the remainder were all
with them. (6)

10Then they took wives, each choosing for himself; whom they began to approach, and with whom they cohabited; teaching them sorcery,  incantations, and the dividing of roots and trees.
11And the women conceiving brought forth giants.

1Moreover Azazyel taught men to make swords, knives, shields, breastplates, the fabrication of mirrors, and the workmanship of bracelets and ornaments, the use of paint, the beautifying of the eyebrows, the use of stones of every valuable and select kind, and all sorts of dyes, so that the world became altered.
2Impiety increased; fornication multiplied; and they transgressed and corrupted all their ways.
3Amazarak taught all the sorcerers, and dividers of roots:
4Armers taught the solution of sorcery;
5Barkayal taught the observers of the stars, (9)
6Akibeel taught signs;
7Tamiel taught astronomy;
8And Asaradel taught the motion of the moon.

From the Book of Jubilees: (written in 2nd BC by Jewish Scribe)

And it came to pass when the children of men began to multiply on the face of the earth and daughters were born unto them, that the angels of God 4 saw them on a certain year of this jubilee, that they were beautiful to look upon; and they took themselves wives of all whom they chose, and they bare unto them sons and they were giants.

And against the angels whom He (God) had sent upon the earth (to watch over men), He was exceedingly wroth, and He gave commandment to root them out of all their dominion, and He bade us to bind them in the depths of the earth, and behold they are bound in the midst of them, and are (kept) separate. 7. And against their sons went forth a command from before His face that they should be smitten with the sword, and be removed from under heaven. 8. And He said “Thy spirit will not always abide 7 on man; for they also are flesh and their days shall be one hundred and twenty years.” 9. And He sent His sword into their midst that each should slay his neighbour, and they (giants) began to slay each other till they all fell by the sword and  were destroyed from the earth. 10. And their fathers were witnesses (of their destruction), and after this they were bound in the depths of the earth for ever, until the day of the great  condemnation 8 when judgment is executed on all those who have corrupted their ways and their works before the Lord.

From Ginsberg Legends of the Jews (a compilation from all Jewish Literature):

The depravity of mankind, which began to show itself in the time of Enosh, had increased monstrously in the time of his grandson Jared, by reason of the fallen angels. When the angels saw the beautiful, attractive daughters of men, they lusted after them, and spoke: “We will choose wives for ourselves only from among the daughters of men, and beget children with them.” Their chief Shemhazai said, “I fear me, ye will not put this plan of yours into execution, and I alone shall have to suffer the consequences of a great sin.” Then they answered him, and said: “We will all swear an oath, and we will bind ourselves, separately and  together, not to abandon the plan, but to carry it through to the end.”

Two hundred angels descended to the summit of Mount Hermon, which owes its name to this very occurrence, because they bound themselves there to fulfil their purpose, on the penalty of Herem, anathema. Under the leadership of twenty captains they defiled themselves with the daughters of men, unto whom they taught charms, conjuring formulas, how to cut roots, and the efficacy of plants. The issue from these mixed marriages was a race of giants, three  thousand ells tall, who consumed the possessions of men. When all had vanished, and they could obtain nothing more from them, the giants turned against men and devoured many of them, and the remnant of men began to trespass against the birds, beasts, reptiles, and fishes, eating their flesh and drinking their blood.

Then the earth complained about the impious evil-doers. But the fallen angels continued to corrupt mankind. Azazel taught men how to make slaughtering knives, arms, shields, and coats of mail. He showed them metals and how to work them, and armlets and all sorts of trinkets, and the use of rouge for the eyes, and how to beautify the eyelids, and how to ornament themselves with the rarest and most precious jewels and all sorts of paints. The chief of the  fallen angels, Shemhazai, instructed them in exorcisms and how to cut roots; Armaros taught them how to raise spells; Barakel, divination from the stars; Kawkabel, astrology; Ezekeel, augury from the clouds; Arakiel, the signs of the earth; Samsaweel, the signs of the sun; and Seriel, the signs of the moon.[57]

While all these abominations defiled the earth, the pious Enoch lived in a secret place. None among men knew his abode, or what had become of him, for he was sojourning with the angel watchers and holy ones. Once he heard the call  addressed to him: “Enoch, thou scribe of justice, go unto the watchers of the heavens, who have left the high heavens, the eternal place of holiness, defiling themselves with women, doing as men do, taking wives  unto themselves, and casting themselves into the arms of destruction upon earth. Go and proclaim unto them that they shall find neither peace nor pardon. For every time they take joy in their offspring, they shall see the violent death of their sons, and sigh over the ruin of their children. They will pray and supplicate evermore, but never shall they attain to mercy or peace.”

(God then tells Enoch) “”Go forth and say to the watchers of heaven….why did you  forsake the high, holy, and eternal heavens, to pollute yourselves with the daughters of men, taking wives unto yourselves, doing like the races of the earth, and begetting giant sons? Giants begotten by flesh and spirits will be called evil spirits on earth, and on the earth will be their dwelling-place. Evil spirits proceed from their bodies, because they are created from above, and from the holy watchers is their beginning and primal origin; they will be evil spirits on earth, and evil spirits they will be named.

And these spirits will rise up against the children of men and against the women, because they have proceeded from them… thus will they destroy until the day when the great consummation of the great world be consummated.

From Hebrew Myths:  The Book of Genesis (Graves/Patai):

By the tenth generation, Adam’s race had hugely increased. Lacking female company, the angels known as “Sons of God” found wives among the lovely Daughters of Men. The children of their unions would have inherited eternal life from their father, but that God had decreed: “Let not My spirit abide in flesh for ever! Henceforth the years of man are limited to one hundred and twenty.”
(b) These new creatures were giants, known as “the Fallen Ones,” whose evil ways decided God to wipe from the face of the earth all men and women, with their gigantic corruptors.1

(c) The Sons of God were sent down to teach mankind truth and justice; and for three hundred years did indeed teach Cain’s son Enoch all the secrets of  Heaven and Earth. Later, however, they lusted after mortal women and defiled themselves by sexual intercourse. Enoch has recorded not only their divine instructions, but also their subsequent fall from grace; before the end they were indiscriminately enjoying virgins, matrons, men, and beasts.2
(d) Some say that Shemhazai and Azael, two angels in God’s confidence, asked: “Lord of the Universe, did we not warn You on the Day of Creation that man would prove unworthy of Your world?” God replied: “But if I destroy man, what will become of My world?” They answered: “We shall inhabit it.” God answered: “Yet upon descending to earth, will you not sin even worse than man?” They
pleaded: “Let us dwell there awhile, and we will sanctify Your name!” God allowed them to descend, but they were at once overcome by lust for Eve’s daughters, Shemhazai begeting on them two monstrous sons named Hiwa and Hiya.  Azael also invented the ornaments and cosmetics employed by women to lead men astray. God therefore warned them that He would set loose the Upper Waters, and thus destroy all men and beasts. Shemhaza wept bitterly, fearing for his sons who, though tall enough to escape drowning, would starve to death.

Afterwards Shemhazai repented, and set himself in the southern sky, between Heaven and Earth – head, down, feet up, and hangs there to this day: the constellation  called Orion by the Greeks.
(g) Azael, however, far from repenting, still offers women ornaments and many-colored robes with which to lead men astray. For this reason, on the Day of Atonement, Israel’s sins are heaped on the annual scapegoat; it is then thrown over a cliff to Azazel – as some call Azael.

(i) The Fallen Ones had such huge appetites that God rained manna upon them, of many different flavours, lest they might be tempted to eat flesh, a forbidden diet, and excuse the fault by pleading scarcity of corn and pot herbs.  Nevertheless, the Fallen Ones rejected God’s manna, slaughtered animals for food, and even dined on human flesh, thus fouling the air with sickly vapours.  It was then that God decided to cleanse Earth.7

From the Works of Josephus (A Jewish Historian in the the time of the destruction of the second Temple):

For many angels(11) of God accompanied with women, and begat sons that proved unjust, and despisers of all that was good, on account of the confidence they had in their own strength; for the tradition is, that these men did what resembled the acts of those whom the Grecians call giants.

But Noah was very uneasy at what they did; and being displeased at their conduct, persuaded them to change their dispositions and their acts for the better: but seeing they did not yield to him, but were slaves to their wicked pleasures, he was afraid they would kill him, together with his wife and children, and those they had married; so he departed out of that land.
2. Now God loved this man for his righteousness: yet he not only condemned
those other men for their wickedness, but determined to destroy the whole race of mankind, and to make another race that should be pure from wickedness; and cutting short their lives, and making their years not so many as they formerly lived, but one hundred and twenty only,(12) he turned the dry land into sea; and thus were all these men destroyed: but Noah alone was saved

From Justin Martyr Second Apology (Early Christian apologetic):

But if this idea take possession of some one, that if we acknowledge God as our helper, we should not, as we say, be oppressed and persecuted by the wicked; this, too, I will solve. God, when He had made the whole world, and subjected things earthly to man, and arranged the heavenly elements for the increase of fruits and rotation of the seasons, and appointed this divine law—for these things also He evidently made for man—committed the care of men and of all things under heaven to angels whom He appointed over them. But the angels transgressed this appointment, and were captivated by love of women, and begat children who are those that are called demons; and besides, they afterwards subdued the human race to themselves, partly by magical writings, and partly by fears and the punishments they occasioned, and partly by teaching them to offer sacrifices, and incense, and libations, of which things they stood in need after they were enslaved by lustful passions; and among men they sowed murders, wars, adulteries, intemperate deeds, and all wickedness. Whence also the poets and mythologists, not knowing that it was the angels and those demons who had been begotten by them that did these things to men, and women, and cities, and nations, which they related, ascribed them to god himself, and to those who were accounted to be his very offspring, and to the offspring of those who were called his brothers, Neptune and Pluto, and to the children again of these their offspring. For  whatever name each of the angels had given to himself and his children, by that name they called them.

From the Apocalypse of Baruch:

5 And as you did previously see on the summit of the cloud black waters which  descended previously on the earth, this is the transgression wherewith Adam
the first man transgressed. 6 For [since] when he transgressed Untimely death
came into being, Grief was named And anguish was prepared, And pain was created, And trouble consummated, And disease began to be established, And Sheol kept demanding that it should be renewed in blood, And the begetting of children was brought about, And the passion of parents produced, And the greatness of humanity was humiliated, And goodness languished. 7 What therefore can be blacker or darker
than these things? 8 This is the beginning of the black waters which you have seen.
9 And from these black (waters) again were  black derived, and the darkness of darkness was produced. 10 For he became a danger to his own soul: even to the angels11 For, moreover, at that time when he was created, they enjoyed liberty. 12 And became he a danger some of them descended, and mingled with the women. 13 And then those who did so were tormented in chains. 14 But the rest of the multitude of the  angels, of which there is (no) number, restrained themselves. 15 And those who dwelt on the earth perished together (with them) through the waters of the deluge. 16 These are the black first waters.