'Angel of the Lord' in the Bible

But in the night an angel of the Lord, opening the doors of the prison, took them out and said,

But an angel of the Lord said to Philip, Get up, and go to the south, to the road which goes from Jerusalem to Gaza, through the waste land.

He saw in a vision, clearly, at about the ninth hour of the day, an angel of the Lord coming to him and saying to him, Cornelius!

And a great light was seen shining in the room, and an angel of the Lord came to Peter and, touching him on his side so that he came out of his sleep, said, Get up quickly. And his chains came off his hands.

And straight away the angel of the Lord sent a disease on him, because he did not give the glory to God: and his flesh was wasted away by worms, and so he came to his end.