Although Manicheism — the religion founded by the Mesopotamian prophet Mani — is dead, its influence still continues in subtle and indirect ways.A nice summary of the career and influence of Mani. Mani, incidentally, included a version of the Book of Giants among his scriptures and we have fragments of it in translations into various medieval Manichean (Manichaean) languages.
Some past posts involving Mani and (mostly) Manichaeism are here, here, here, here, here, here, here, here, here, and here.