The Nephilim were on the earth at that time (and also immediately afterward), when those divine beings were having sexual relations with those human women, who gave birth to children for them. These children became the heroes and legendary figures of ancient times.

that they are greatly afraid, because Gibeon is a great city, as one of the royal cities, and because it is greater than Ai, and all its men -- heroes.

And Hushai saith, 'Thou hast known thy father and his men, that they are heroes, and they are bitter in soul as a bereaved bear in a field, and thy father is a man of war, and doth not lodge with the people;

These are the names of the mighty men (warriors) whom David had: Josheb-basshebeth, a Tahchemonite, chief of the captains, also called Adino the Eznite (spear) because of the eight hundred men killed [by him] at one time.

Adina the son of Shiza the Reubenite, a chief of the Reubenites, and thirty [heroes] with him,

Bless Yahweh, you his angels, [you] mighty heroes who do his word by {obeying} the sound of his word.

Woe to those who are heroes at drinking wine,who are fearless at mixing beer,

Look! Their heroes cry out [in the] street; [the] messengers of peace weep bitterly.

“Their quiver is [filled with the dead] like an open grave;They are all mighty men [heroes of their nation].

How can you men of Moab say, 'We are heroes, men who are mighty in battle?'

Nor do they lie beside the fallen heroes of the uncircumcised, who went down to Sheol with their weapons of war and whose swords were laid under their heads; but the punishment for their iniquity rested on their bones, though the terror of these heroes was once in the land of the living.

And they have been as heroes, Treading in mire of out-places in battle, And they have fought, for Jehovah is with them, And have put to shame riders of horses.

because God had us in mind and had something better for us, so that they [these men and women of authentic faith] would not be made perfect [that is, completed in Him] apart from us.