'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.

Then the angel of the Lord spake unto Philip, saying, "Arise and go towards midday unto the way that goeth down from Jerusalem unto Gaza, which is in the desert."

And behold, the angel of the Lord was there present, and a light shined in the lodge. And he smote Peter on the side, and stirred 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 honour, and he was eaten of worms, and gave up the ghost.