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
Some studies of David have been written: Baruch Halpern has pictured David as a lifelong vassal of Achish, the Philistine king of Gath; Israel Finkelstein and Neil Asher Silberman have identified as the oldest and most reliable section of Samuel those chapters which describe David as the charismatic leader of a band of outlaws who captures Jerusalem and makes it his capital. Steven McKenzie, Associate Professor of the Hebrew Bible at Rhodes College and author of "King David: A Biography", argues that David came from a wealthy family, was "ambitious and ruthless" and a tyrant who murdered his opponents, including his own sons.