He was a giant Philistine warrior defeated by the young David, the future king of Israel - the story is told in the Bible's Books of Samuel.
As Goliath moved in for the kill, David reached into his bag and slung one of his stones at Goliath's head. Finding a hole in the armor, the stone sank into the giant's forehead, and he fell face down on the ground. David then took Goliath's sword, killed him and then cut off his head. When the Philistines saw that their hero was dead, they turned and ran. So the Israelites pursued, chasing and killing them and plundering their camp.