Angel of the Lord

In Luke 1:9 the angel of the Lord makes the announcement of Christ birth. Who is he? In the O. T. he made several appearance. Many be live he is a personal visible manifestation of Christ Himself. Christ is in the manger being born and on the hill side telling the shepherds of His own birth. How can this be? He is all God and all man. He told Nicodemus in John 3:13. I’m the one who came down from heaven and in heaven at the same time. My! My! what a saviour.