20:1 angel. The angel may well be the Lord Jesus Christ Himself, since it is He who has the key to the bottomless pit (Revelation 1:18), and it would be most appropriate for the Son, on behalf of the Father, to personally dispatch the great rebel to his prison.
20:1 bottomless pit. On the bottomless pit (Greek abusos) see note on Revelation 9:1. The demons had dreaded the prospect of being sent by Christ to “the deep” (same Greek word, Luke 8:31), but the “time” for their “torment” (Matthew 8:29) will finally have come, as they will be corralled with their evil prince into the deep dungeon.
20:1 great chain. The “great chain,” with which to “bind the strong man” (Mark 3:27) is no doubt a spiritual chain to restrain the spirit being called Satan, but it will serve the purpose, whatever it is.