'Angel of the Lord' in the Bible

But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.

Then Joseph being raised from sleep did as the angel of the Lord had bidden him, and took unto him his wife:

And when they were departed, behold, the angel of the Lord appeareth to Joseph in a dream, saying, Arise, and take the young child and his mother, and flee into Egypt, and be thou there until I bring thee word: for Herod will seek the young child to destroy him.

But when Herod was dead, behold, an angel of the Lord appeareth in a dream to Joseph in Egypt,

And, behold, there was a great earthquake: for the angel of the Lord descended from heaven, and came and rolled back the stone from the door, and sat upon it.