The Book of Enoch (also known as 1 Enoch), is an ancient Jewish religious work, ascribed by tradition and internal attestation to Enoch, the great-grandfather of Noah.[1][2] 1 Enoch holds material unique to it, such as the origins of supernatural demons and giants, why some angels fell from heaven, details explaining why the Great Flood was morally necessary, and an introduction of the thousand-year reign of the Messiah.[3][2] The unique material makes it possible to identify which ancient literary works adopt 1 Enoch as a source. Well known in antiquity, the book was received by various authors with respect, and sometimes considered as divinely inspired.[1][2]