Acts 7:v.30-38 reveals who was him:
30 And when forty years were expired, there appeared to him in the wilderness of mount Sina an angel of the Lord (actually an Archangel) in a flame of fire in a bush.
31 When Moses saw it, he wondered at the sight: and as he drew near to behold it, the voice of the Lord came unto him,
32 Saying, I am the God of thy fathers, the God of Abraham, and the God of Isaac, and the God of Jacob*. Then Moses trembled, and durst not behold. (Compare with
33 Then said the Lord to him, Put off thy shoes from thy feet: for the place where thou standest is holy ground.
34 I have seen, I have seen the affliction of my people which is in Egypt, and I have heard their groaning, and am come down to deliver them. And now come, I will send thee into Egypt.
35 This Moses whom they refused, saying, Who made thee a ruler and a judge? the same did God send to be a ruler and a deliverer by the hand of the angel which appeared to him in the bush.
36 He brought them out, after that he had shewed wonders and signs in the land of Egypt, and in the Red sea, and in the wilderness forty years.
37 This is that Moses, which said unto the children of Israel, A prophet shall the Lord your God raise up unto you of your brethren, like unto me; him shall ye hear.
38 This is he, that was in the church in the wilderness with the angel which spake to him in the mount Sina, and with our fathers: who received the lively oracles to give unto us:
* I am the God of thy fathers, the God of Abraham, and the God of Isaac, and the God of Jacob
20 Behold, I send an Angel before thee, to keep thee in the way, and to bring thee into the place which I have prepared.
21 Beware of him, and obey his voice, provoke him not; for he will not pardon your transgressions: for my name is in him.*
22 But if thou shalt indeed obey his voice, and do all that I speak; then I will be an enemy unto thine enemies, and an adversary unto thine adversaries.
23 For mine Angel (actually an Archangel) shall go before thee, and bring thee in unto the Amorites, and the Hittites, and the Perizzites, and the Canaanites, the Hivites, and the Jebusites: and I will cut them off.