The first two kings, Saul and David, feature prominently in the first book of Samuel.
The First Book of Samuel is the ninth book in the Bible. It tells us about the prophet Samuel and the transition of Israel from the rule of Judges to that of Kings.
I Samuel 17:49-51
"And David put his hand in his bag, and took thence a stone, and slang it, and smote the Philistine in his forehead, that the stone sunk into his forehead; and he fell upon his face to the earth. So David prevailed over the Philistine with a sling and with a stone, and smote the Philistine, and slew him; but there was no sword in the hand of David. Therefore David ran, and stood upon the Philistine, and took his sword, and drew it out of the sheath thereof, and slew him, and cut off his head therewith. And when the Philistines saw their champion was dead, they fled"