"Ogias the Giant, also known as The Book of Giants is one of the books from the New Testament apocrypha which concerned the Old Testament. The text relates how before the great flood, there was a giant named Ogias who fought a great dragon. A brief mention of this giant, "Ohia" is found in the Babylonian Talmud (Nidah, Ch 9), where it is said "Sihon and Og [from the book of Genesis] were brothers, as they were the sons of Ohia the son of Semjâzâ [one of the leaders of the fallen angels in the Book of Enoch]".

The book is thought to have been based on the Book of Enoch, itself based on an obscure passage from Genesis (6:1-4) concerning Nephilim, which became "fallen angels". The book concerns itself with filling in the details about the giants and their offspring that the book of Enoch misses out. Aramaic fragments of it, along with other fragments of the Book of Enoch, were found among the Dead Sea Scrolls at Qumran. In the version of the Book of Giants which was spread by the Manichaean religion, the book became well travelled, and exists in Syriac, Greek, Persian, Sogdian, Uyghur, and Arabic, although each version is somewhat distorted, incorporating more local myths.

The version found at Qumran also describes the hero Gilgamesh and the monster Humbaba as two of the giants accompanying Ogias.