Goliath
Goliath is described in the biblical Book of Samuel as a Philistine giant defeated by the young David in single combat. The story signified Saul's unfitness to rule, as Saul himself should have fought for the Kingdom of Israel.
David
God is angered when Saul, Israel's king, unlawfully offers a sacrifice and later disobeys a divine command both to kill all of the Amalekites and to destroy their confiscated property. Consequently, God sends the prophet Samuel to anoint a shepherd, David, the youngest son of Jesse of Bethlehem, to be king instead.
After God sends an evil spirit to torment Saul, his courtiers recommend that he send for David, a man skillful on the lyre, wise in speech, and brave in battle. David thus enters Saul's service as one of the royal armour-bearers and plays the lyre to soothe the king.
War comes between Israel and the Philistines, and the giant Goliath challenges the Israelites to send out a champion to face him in single combat. David, sent by his father to bring provisions to his brothers serving in Saul's army, declares that he can defeat Goliath. Refusing the king's offer of the royal armour, he kills Goliath with his sling. Saul inquires the name of the young hero's father.