John had described each of these three in detail in Revelation 12—13. The dragon is that ancient serpent, who is called the devil and Satan
who had been thrown out of heaven and so in great wrath went off to make war on God’s people
(Revelation 12:9, Revelation 12:17).
The beast is the hideous collaborator described in Revelation 13:1–10 to whom the dragon gave his power and his throne and his authority
and whom God allowed to make war on the saints and to conquer them
(Revelation 13:2, Revelation 13:7). It was on the throne of this beast that the fifth angel poured his bowl (Revelation 16:10–11).
The false prophet is the second beast of Revelation 13:11–18 who “spoke like a dragon” and deceived people by telling them to worship the first beast (Revelation 13:11, Revelation 13:14).
13 And I saw, coming out of the mouth of the dragon and out of the mouth of the beast and out of the mouth of the false prophet, three unclean spirits like frogs.