Who are the Giants?

I was asked recently: Who are the giants of Genesis 6, prior to the flood? and what are these Nephaliym?

There are typically taught 2 views concerning this:

(1) That the giants are the offspring of fallen angels having relations with human females.

(2) That the offspring of sons of God and daughters of men are sons of the godly line of Seth procreating with ungodly, sinful women from the line of
Cain.

The answer may surprise many...