In revelation 16 John sees three unclean spirits come out of the false prophet, the beast and the dragon. Could the dragon be an extraterrestrial/ angel or even a physical embodiment of Satan himself? In the passage he clearly is represented as a third person in the unholy trinity.
The dragon mentioned in Rev. 16:13 is the one introduced in Rev. 12 and spoken of several times there and afterward. In Rev. 12:9 he’s identified as “that ancient serpent, called the devil, or Satan, who leads the whole world astray.”