'Angel of the Lord' in the Bible

But the angel of the Lord by night opened the prison doors, and brought them forth, and said,

And when forty years were expired, there appeared to him in the wilderness of mount Sinai an angel of the Lord in a flame of fire in a bush.

And the angel of the Lord spoke unto Philip, saying, Arise, and go toward the south unto the way that goes down from Jerusalem unto Gaza, which is desert.

And, behold, the angel of the Lord came upon him, and a light shined in the prison: and he struck Peter on the side, and raised him up, saying, Arise up quickly. And his chains fell off from his hands.

And immediately the angel of the Lord smote him, because he gave not God the glory: and he was eaten of worms, and died.