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

Then the leaders of the Philistines said, "What about these Hebrews?" And Achish said to the leaders 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?"