'King of Israel' in the Bible

Against whom has the king of Israel come out? Whom do you pursue? A dead dog? A flea?

Now therefore, don't let my blood fall to the earth away from the presence of Yahweh; for the king of Israel has come out to seek a flea, as when one hunts a partridge in the mountains."

Then the princes of the Philistines said, "What about these Hebrews?" Achish said to the princes of the Philistines, "Isn't this David, the servant of Saul the king of Israel, who has been with me these days, or rather these years, and I have found no fault in him since he fell away to this day?"