'King of Israel' in the Bible

After whom did the king of Israel come forth? after whom pursuest thou? after a dead dog? after one flea?

And now my blood shall not fall to the earth from before the face of Jehovah; for the king of Israel came forth to seek one flea, as when the partridge will pursue in the mountains.

And the chiefs of the rovers will say, What these Hebrews? and Achish will say to the chiefs of the rovers, Is not this David, servant of Saul king of Israel, who was with me these days or these years, and I found nothing in him from the day of his falling till this day