The Book Of Enoch:

And they took as their wives any they chose. . . . The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of man and they bore children to them. These were the mighty men who were of old, the men of renown. (Genesis 6:1-4) Enoch, the son of Jared and seventh from Adam, is the most eminent pre-Flood patriarch in the annals of ancient Israel, and yet, paradoxically, the Hebrew scriptures have almost nothing to say concerning him. There can be no doubt that the Jews regarded Enoch as a holy scribe and prophet, indeed, the first and foremost on both accounts, but not a single word is attributed to him in the Old Testament. One is left to wonder, If Enoch is a scribe, then what did he write? And if a prophet, what did he prophesy? The answers to these questions are revealed in the Book of Enoch. Preserved for centuries by the Ethiopians, and discovered among the Dead Sea Scrolls in the Caves of Qumran, the Book of Enoch is an epic narrative concerning the world before the Flood of Noah. Laced with messianic prophecies, apocalyptic themes, and esoteric visions, the Enochian tale recounts the fall of the Watchers—a renegade group of angels who impregnated human women, progenerated man-eating giants, and disclosed forbidden knowledge from heaven that wreaked havoc on Earth. Enoch lays an essential foundation for understanding the origin of Nephilim and demons in the biblical text, and offers a unique window into the religious and intellectual currents of the Second Temple period. After centuries of suppression and obscurity, the Book of Enoch has resurfaced in our time and is enjoying a renewed interest among scholars and ordinary readers alike, who are rediscovering the Hebraic perception of the pre-Flood world and the extraordinary events that precipitated its cataclysmic destruction.