Goliath was a famous giant of Gath and champion solider of the Philistines. When the armies of the Philistines and the Israelites faced each other across the valley of Elah, Goliath challenged Saul's army.
Goliath stood and shouted to the ranks of Israel, "Why do you come out and line up for battle? Am I not a Philistine, and are you not the servants of Saul? Choose a man and have him come down to me. If he is able to fight and kill me, we will become your subjects; but if I overcome him and kill him, you will become our subjects and serve us." (1 Samuel 17:8-9)
The Israelites were terrified by his challenge which went on for forty days, before David a young shepherd boy took him on. David had arrived at the Israelite camp with some food for his brothers who were soldiers in the army and was amazed that nobody would fight Goliath. He said that he would, and when King Saul heard of the shepherd boy's boast he sent for him.
Saul replied, "You are not able to go out against this Philistine and fight him; you are only a boy, and he has been a fighting man from his youth."
But David said to Saul, "Your servant has been keeping his father's sheep. When a lion or a bear came and carried off a sheep from the flock, I went after it, struck it and rescued the sheep from its mouth. When it turned on me, I seized it by its hair, struck it and killed it. Your servant has killed both the lion and the bear; this uncircumcised Philistine will be like one of them, because he has defied the armies of the living God.
(1 Samuel 17:33-36)
Saul gave David his blessings and his armor, but it was too big for the young lad. Instead, he advanced toward Goliath with just a staff, a sling and five smooth stones. After a brief chat with the giant - mainly involving the trading of insults - he ran toward Goliath, put a stone in his sling and threw it with all his might. It hit Goliath in the middle of the forehead and stunned the giant, who fell to the ground. Immediately, David raced to him, drew out Goliath's sword and cut his head off.
When the Philistines saw that their hero was dead they turned and ran with the Israelites in hot pursuit. David's victory over Goliath was the turning point in his life. He came into the public eye as the deliverer of Israel and the chief among Saul's men of war.