"The Nephilim proved to be in the earth in those days, AND ALSO AFTER THAT, when the sons of the true God continued to have relations with the daughters of men and they bore sons to them, they were the mighty ones who were of old, the men of fame."
Several suggestions as to the identity of these Nephilim have been offered:
Some Bible commentators have thought that the derivation of the name indicates that the Nephilim had fallen from heaven, that is, that they were ‘fallen angels’ (1 Pet. 3:19,20) who mated with women to produce "mighty ones . . . the men of fame." One problem with this is, how can non-gender angels mate with women?
Other scholars, focusing their attention particularly on the statement "and also after that" (vs 4), have said the Nephilim were not the ‘fallen angels’ or the "mighty ones," since the Nephilim "proved to be in the earth in those days" BEFORE the sons of God had relations with women. These latter scholars hold the opinion that the Nephilim were simply wicked men like Cain—robbers, bullies, and tyrants who roamed the earth until they were destroyed by the Flood.
Still another group, taking into consideration the context of verse 4, conclude that the Nephilim were not themselves angels, but were the hybrid offspring resulting from materialized angels (angels taking human form) having intercourse with the daughters of men.
This last group of scholars seem closest to defining the true identity of the Nephilim when considering the Biblical context.
For more, see
ANGELS - How They Affect Us (Scroll to Subheading, "Demons—Who Are They?")
Search For Bible Truths - ARCHIVE
Search For Bible Truths - Search Guide