The Lord has not identified this angel and so his identity is not important for us. Important is that all angels are ministering servants sent forth by God to serve those who are to obtain salvation (Hebrews 1:14; Psalm 103:20–21). This angel, then, did not come down on his own initiative but came upon the Lord’s command. Presumably, heaven was still standing wide open (Revelation 19:11). His “coming down” indicates he travelled to our planet (Revelation 12:9).
1 Then I saw an angel coming down from heaven, holding in his hand the key to the bottomless pit and a great chain.