'Angel of the Lord' in the Bible

But the angel of the LORD said to Elijah the Tishbite, Arise, go up to meet the messengers of the king of Samaria, and say to them, Is it not because there is not a God in Israel, that ye go to inquire of Baal-zebub the god of Ekron?

And the angel of the LORD said to Elijah, Go down with him: be not afraid of him. And he arose, and went down with him to the king.

And it came to pass that night, that the angel of the LORD went out, and smote in the camp of the Assyrians a hundred and eighty five thousand: and when they arose early in the morning, behold, they were all dead corpses.