'Angel of the Lord' in the Bible

But the Angel of the LORD spake to Elijah the Tishbite, "Up, and go against the messengers of the king of Samaria and say unto them, 'Is it because there is no God in Israel, that ye go to ask through Beelzebub the god of Ekron?

Then said the Angel of the LORD unto Elijah, "Go down with him, and be not afraid of him." And he went down with him unto the king.

And the selfsame night the Angel of the LORD went out and smote, in the host of the Assyrians, a hundred and four score and five thousand. And when they were up early in the morning: behold, they were all dead corpses.