The Angel of the Lord (sometimes "of God") is a special angel in the Old Testament. Sometimes he shows up on the scene to deliver an message or to provide protection. Frequently he speaks in the first person singular ("I"), just as if he himself were God.
Some scholars say that this angel was God's personal messenger and could speak as though he were God. But I know in my spirit that this is the pre-incarnate Christ! The Angel of the Lord is the Lord Jesus Christ before He was born of the virgin and made flesh.
One time He announced Himself as "Captain of the host of the Lord." Now there were several captains of hosts mentioned in the OT but only once is there a Captain of the host of the LORD. It was Jesus in that barley field with Joshua! (Josh. 5:13)
To whom did he appear?
To Hagar when she ran away from Sarai; and when she thought Ishmael was going to die -- Gen. 16:7f; 21:17
To Abraham at the offering of Isaac -- Gen. 22:11, 15
To Jacob when he was watching the livestock breed -- Gen. 31:11-13
To Moses in a flame of fire out of the midst of a bush -- Ex. 3:2
To the Israelites in a pillar of fire between them and the Egyptians at the exodus -- Ex. 14:19
To Balaam's ass, and then to Balaam -- Num. 22:22-36
To Joshua before Jericho -- Josh. 5:13
Called Gideon a mighty man of valor; Gideon's reply was, "who me?" -- Jdg. 6.11ff
To Samson's Mom & Dad -- Jdg. 13:21 22
Caused David to pay full price for a threshing floor -- 1 Chr. 21:16
Sent Elijah to the messengers of Ahaziah, king of Samaria -- 2 Kings 1:3-6
To Daniel to shut the mouths of lions -- Dan. 6:22
What does he do when he comes on the scene?
Delivered messages from the Lord -- Gen. 22:15-18
Protected God's people -- 2 Kings 19:34-35
Redeemed God's people -- Isa. 63:9
Punished God's people -- 2 Sam. 24:16-17
Destroyed God's enemies -- Ex. 23:23
How can we identify him as God (Jesus)?
He uses "I" when he brings a message -- Gen. 16:10; 22:16-17; 31:13; Ex. 3:6; Jdg. 6:14
He describes himself as holy -- Ex. 3:2.5
He carries out God's judgment -- 2 Sam. 24:16; 2 Kings 19:35
God's name is in him -- Ex. 23:20-23
He shows up as a man -- Josh. 5:13-15; Jdg. 13:6, 10, 21