The following is one of two places in the Old Testament where the KJV translators failed to bring the word Rephaim, which was a name for the giants, into the English.
Isa 26:14
14 They are dead, they shall not live; they are deceased ('rapha', i.e., Rephaim), they shall not rise: therefore hast Thou visited and destroyed them, and made all their memory to perish.
KJV
The giants were hybrid offspring, not simply bully tyrants. Even normal men born through woman that are wicked will have a resurrection ("resurrection of damnation" of John 5:28-29). But these Rephaim (giants) will not. They shall not rise. That is one of the definite Bible proofs that the Rephaim, i.e., giants, were a literal hybrid offspring that God did not create.
Genesis 6 says they were "mighty men which were of old, men of renown". That idea of "men of renown" means men of the legend. What legend?
The ancient mythologies of gods on the earth among the ancients. Many ancient nation's histories record of those, including the American Indian culture.
Buffalo Bill's report from a Pawnee Indian that brought him bones of a hybrid giant:
"While we were in the sand hills, scouting the Niobrara country, the Pawnee Indians brought into camp some very large bones, one of which the surgeon of the expedition pronounced to be the thigh-bone of a human being. The Indians claimed that the bones they had found were those of a person belonging to a race of people who a long time ago lived in this country; that there was once a race of men on the earth whose size was about three times that of an ordinary man, and they were so swift and powerful that they could run along-side of a buffalo, and taking the animal in one arm could tear off a leg and eat the meat as they walked." ("The Life Of The Honorable William F. Cody", by William F. Cody, 1879.)