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
Apart from these, all that is known of David comes from the biblical literature. The Books of Samuel were substantially composed during the time of King Josiah at the end of the 7th century BCE, extended during the Babylonian exile (6th century BCE), and substantially complete by about 550 BCE, although further editing was done even after then—the silver quarter-shekel which Saul's servant offers to Samuel in 1 Samuel 9 "almost certainly fixes the date of the story in the Persian or Hellenistic period". The authors and editors of Samuel drew on many earlier sources, including, for their history of David, the "history of David's rise" (1 Samuel 16:14–2 Samuel 5:10), and the "succession narrative" (2 Samuel 9–20 and 1 Kings 1–2). The Book of Chronicles, which tells the story from a different point of view, was probably composed in the period 350–300 BCE, and uses Samuel as its source.