The origination of the Nephilim begins with a story of the fallen angels. Shemhazai, an angel of high rank, led a sect of angels in a descent to earth to instruct humans in righteousness. The tutelage went on for a few centuries, but soon the angels pined for the human females. After lusting, the fallen angels instructed the women in magic and conjuring, mated with them, and produced hybrid offspring: the Nephilim.
The Nephilim were gigantic in stature. Their strength was prodigious and their appetites immense. Upon devouring all of humankind's resources, they began to consume humans themselves. The Nephilim attacked and oppressed humans and were the cause of massive destruction on the earth.
Two texts of central import to the story of the Nephilim, the Bible and the Dead Sea Scrolls, mention several names for the Nephilim. The diverse kinds of these giants are cited in several passages. They are variously referred to as Emim, or "Terrors" (Gen. 14:5; Deut. 2:10), Rephaim, or "Weakeners" or "Dead Ones" (2 Sam. 23:13; 1 Chron. 11:15), Gibborim, or "Giant Heroes" (Job 16:4), Zamzummim, or "Achievers" (Deut. 2:10), Anakim, or "Long-necked" (Deut. 2:10; Josh. 11:22, 14:15), and Awwim or "Devastators" and "Serpents." Other giants are mentioned in these texts as well, such as Goliath (2 Sam. 21:19), a giant with twelve fingers and twelve toes who is mentioned as one of the Rephaim (2 Sam. 21:20), and a tall Egyptian (1 Chron. 11:23). The passage of Numbers 13:26-33 recounts the Nephilim of Canaan that Joshua and the other Hebrew spies saw. Furthermore, according to Judaic lore, a certain one of the Nephilim, Arba, built a city, Kiriath Arba, which was named for its builder and is now known as Hebron.
The wickedness of the Nephilim carried with it a heavy toll. Genesis 6:5 alludes to the corruption that the Nephilim had caused amongst humans and themselves: "The Lord saw how great man's wickedness on the earth had become..." Their evil rebellion had incurred both the wrath and grief of God. God instructed the angel Gabriel to ignite a civil war among the Nephilim. He also chose Enoch, a righteous man, to inform the fallen angels of the judgment pronounced on them and their children. God did not allow the fallen angels any peace, for they could not lift their eyes to heaven and were later to be chained. The end of the Nephilim came about in the war incited by Gabriel, in which the giants eventually annihilated each other.