Samyaza (Aramaic: שמיחזה, Greek: Σεμιαζά), also Semihazah, Shemyazaz, Shemyaza, Sêmîazâz, Semjâzâ, Samjâzâ, Semyaza, and Shemhazai, is a fallen angel of apocryphal Jewish and Christian tradition that ranked in the heavenly hierarchy as one of the Watchers. The name "Shemyaza(z)" means "the (or my) name has seen" or "he sees the name".
Sins of Samyaza and his associates
And Semjâzâ, who was their leader, said unto them: "I fear ye will not indeed agree to do this deed, and I alone shall have to pay the penalty of a great sin." And they all answered him and said: "Let us all swear an oath, and all bind ourselves by mutual imprecations not to abandon this plan but to do this thing." Then sware they all together and bound themselves by mutual imprecations upon it. (Enoch 6:3-5)
Samyaza convinced several other Watchers to join him in fornicating with women. As a result, he and the other sinful Grigori begot giant offspring (called Nephilim in the Book of Genesis) that dominated and feasted upon humans during the days of Jared. The Watchers' other sin was to teach humans various creative arts — especially Azazel's, who taught the secrets of war, which brought down the wrath of God.
God commanded the angel Gabriel to cause the Giants to wage civil war:
And to Gabriel said the Lord: "Proceed against the biters and the reprobates, and against the children of fornication: and destroy [the children of fornication and] the children of the Watchers from amongst men [and cause them to go forth]: send them one against the other that they may destroy each other in battle: for length of days shall they not have[.] (Enoch 10:9)
Finally, the judgement of the associates of Samyaza is described.
And the Lord said unto Michael: "Go, bind Semjâzâ and his associates who have united themselves with women so as to have defiled themselves with them in all their uncleanness. And when their sons have slain one another, and they have seen the destruction of their beloved ones, bind them fast for seventy generations in the valleys of the earth, till the day of their judgement and of their consummation, till the judgement that is for ever and ever is consummated. In those days they shall be led off to the abyss of fire:〈and〉to the torment and the prison in which they shall be confined for ever. And whosoever shall be condemned and destroyed will from thenceforth be bound together with them to the end of all generations[.] (Enoch 10:11-14)
After the destruction of the Giants, God caused the Great Flood of Noah to wipe out the humans who had become corrupted. (The Holy Bible teaches that they were there before and after the flood, however.)