'King of Israel' in the Bible

After whom is the king of Israel come out? after whom do you 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 has come out to seek a flea, as when one does hunt a partridge in the mountains.

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