The Nephilim were on the earth in those days(and also after this) when the sons of God would sleep with the daughters of humankind, who gave birth to their children. They were the mighty heroes of old, the famous men.
TSK
TSK · 2 Samuel 16:21
مراجع Treasury of Scripture Knowledge في NET.
While Israel was living in that land, Reuben went to bed with Bilhah, his father’s concubine, and Israel heard about it.Jacob had twelve sons:
Reuben, you are my firstborn, my might and the beginning of my strength, outstanding in dignity, outstanding in power.
If a man goes to bed with his father’s wife, he has exposed his father’s nakedness. Both of them must be put to death; their blood guilt is on themselves.
So Achish trusted David, thinking to himself,“He is really hated among his own people in Israel! From now on he will be my servant.”
When the Ammonites realized that David was disgusted with them, they sent and hired 20,000 foot soldiers from Aram Beth Rehob and Aram Zobah, in addition to 1000 men from the king of Maacah and 12,000 men from Ish-tob.
Jonadab replied to him,“Lie down on your bed and pretend to be sick. When your father comes in to see you, say to him,‘Please let my sister Tamar come in so she can fix some food for me. Let her prepare the food in my sight so I can watch. Then I will eat from her hand.’”
Then David went to his palace in Jerusalem. The king took the ten concubines he had left to care for the palace and placed them under confinement. Though he provided for their needs, he did not sleep with them. They remained under restriction until the day they died, living out the rest of their lives as widows.
King Solomon answered his mother,“Why just request Abishag the Shunammite for him? Since he is my older brother, you should also request the kingdom for him, for Abiathar the priest, and for Joab son of Zeruiah!”
And it will come about that just as you(both Judah and Israel) were a curse to the nations, so I will save you and you will be a blessing. Do not be afraid! Instead, be strong!’