Goliath is a man in the Book of Samuel, described as a Philistine giant defeated by the young David in single combat. The story signified King Saul's unfitness to rule, as Saul himself should have fought for Israel. Modern scholars believe that the original slayer of Goliath may have been Elhanan, son of Jair, who features in 2 Samuel 21:19, in which Elhanan kills Goliath the Gittite, and that the authors of the Deuteronomic history changed the original text to credit the victory to the more famous character David.

Source: Wikipedia