'Angel of the Lord' in the Bible

But in the night the angel of the Lord threw open the jail doors and let them out, and said to them,

Now an angel of the Lord said to Philip, "Get up and go south by the road that leads from Jerusalem to Gaza; this is the desert road."

And suddenly an angel of the Lord stood by him, and a light shone in his cell, and by striking Peter on the side the angel woke him, and said, "Get up quickly!" At once the chains fell off his hands.

But the angel of the Lord at once struck him down, because he did not give the glory to God; he was eaten by worms, and so died.