'King of Israel' in the Bible

After whom is the king of Israel come out? after whom dost thou pursue? after a dead dog, after a flea?

Now therefore, let not my blood fall to the earth before the face of the LORD: for the king of Israel hath come out to seek a flea, as when one doth hunt a partridge in the mountains.

Then said the princes of the Philistines, What do these Hebrews here? And Achish said to the princes of the Philistines, Is not this David, the servant of Saul the king of Israel, who hath been with me these days, or these years, and I have found no fault in him since he fell to me to this day?