Are the Nephilim of Genesis 6 the Basis for the Greek Legends of Hercules?
“Basis” is a problematic term. There are similarities, but we need to consider what Genesis is trying to accomplish literarily and theologically in chapter 6.
In Genesis 6:4, we read that in the days before the Flood the “sons of God” took the “daughters of men” as their wives. The Nephilim appear to have been the product of that union – might warriors of ancient times, men of renown. There is far too much discussion about Genesis 6:1-4 to write about succinctly here. Suffice to say that we are not entirely certain who the “sons of God” are meant to refer to, so it is difficult to say what exactly is going on here. It seems to me that this question assumes a particular interpretation of “sons of God”, specifically that they refer to angels, perhaps fallen angels. Therefore, the Nephilim were half-angelic, half-human beings. Demigods, essentially, who would have been not unlike famous Greek mighty men such as Perseus, Achilles, or Hercules. So there is definitely a conceptual similarity between the Nephilim and Hercules, but I’m not sure I’d go so far as to say that the Nephilim are the basis for the legends of Hercules.
So what’s the difference? To say that the Nephilim are the basis for the legends of Hercules implies that the Nephilim story in Genesis 6 is uninterpreted history. In other words, thousands of years ago (before whenever the flood must have happened), the Nephilim thing happened essentially the way Genesis says it did (assuming, again, that the “sons of God” or angelic beings). While Genesis remembers this accurately and unvarnished, it was passed on orally and imperfectly in other cultures, as in Greek culture which eventually remembered the literal history of the Nephilim as ancient hero stories like those of Hercules.
Honestly, literarily there is more of a connection between Hercules and Samson than between Hercules and the Nephilim. Greek literature is full of half-man half-god heroes, not just Hercules. It is kind of a standard Greek motif. A lot of scholarly literature has been written analyzing the similarities between Samson and Hercules (and this is the basis for some people dating the Samson stories to the Hellenistic Period, which I think is absolute hogwash).
But what is the Nephilim passage doing? Why is it in Genesis, since Genesis 1-11 by no means even pretends to be a blow-by-blow historical account of everything that happened in the primeval, pre-flood history of humanity. It serves a literary purpose, and that is the first question you have to ask when seeking to understand things like the Nephilim or the Tower of Babel. On a meta-textual level, it seems to me that the Nephilim passage is an Israelite attempt to subjugate all history and legends to its own history. Within the text itself, the Nephilim can be understood as sort of the straw that broke the camel’s back with regard to God’s decision to destroy the world. So, Genesis says to non-Israelite cultures, not only is Yahweh the God of your demi-god legends, your demi-god was actually a semi-demonic creature who was no hero at all but was actually part of what was wrong with the world before the Flood.
Genesis seems to declare that the Nephilim, as Genesis relates them, were the basis for the hero stories of the surrounding cultures. But are the Nephilim actually the basis for these legends? I think that’s an assertion that cannot possibly be proven. I also think there are other, easier, and more reasonable explanations for how legends like those of Hercules could have arisen from real history. So there is a conceptual connection (especially from the Genesis side), but probably not a genetic one (literarily or historically speaking).