Revelation is difficult to understand, but we must consider Revelation 20:10 (WEB),

The devil who deceived them was thrown into the lake of fire and sulfur, where the beast and the false prophet are also. They will be tormented day and night forever and ever.

Only three people are explicitly named in Scripture as destined to the Lake of Fire.  They are Satan, The Beast, and The False Prophet.

So how do we determine the nature of the members of this Unholy Trinity: The Devil (Satan / Dragon), The Beast (First / Sea Beast), and The False Prophet (Second / Land Beast)?  Are they human beings, demonic beings, or non-being forces?

Everyone agrees that Satan is a demon, a fallen angel.  Well, not everyone agrees.  Mormons are confused about that, suggesting that Satan is actually Jesus' brother.  A few others have defined Satan as the epitome of evil, but that he is in fact not a being, not a person.  However, I easily side with the majority, that Satan is a being, a non-human spirit person with mind, will, and emotion.  He is the Chief fallen angel actively leading his rebellion against God.

However, what about The Beast and The False Prophet?   Revelation 13 introduces both a First Beast from the sea and Second Beast from the land.  A comparison of Revelation 13:14 and 19:20 shows that the Second Beast is later referred to as The False Prophet in Revelation 16:13, 19:20, and 20:10.  Thus the Second Beast and The False Prophet are the same person.

Revelation 16:13-14 also shows us that the mouths of The Dragon (Satan), The Beast, and The False Prophet are each the source of demonic spirits.   This is initial evidence that these three beings share a common nature.  This is one argument that they are not human beings, but instead demonic beings.  Humans do not beget demons, but Satan, The Beast, and The False Prophet are the source of demonic activity.  They are the demon chiefs!

13) 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, something like frogs; 14) for they are spirits of demons, performing signs; which go out to the kings of the whole inhabited earth, to gather them together for the war of that great day of God, the Almighty.

Revelation 16:13-14 (WEB)

Secondly, we already know that Jesus became a human being to pay for the sins of all mankind and thus I have reasoned that all mankind is spared the Lake of Fire.  Jesus did not become an angel and so apparently the sins of fallen angels are not atoned and they will suffer the Lake of Fire.  Thus, those sentenced to the Lake of Fire are demons, fallen angels, and not human beings.  Otherwise, if they were human, their sins would be paid for and they would not be sentenced to the Lake of Fire.  Matthew 25:41, previously mentioned, also clearly states that the Lake of Fire is "prepared for the Devil and his angels."  Jude 6 and 2 Peter 2:4 also make it clear that fallen angels will be present at the final judgment, hence the goats on Jesus' left.

Further study could be done to confirm the identity of The First Beast as demonic.  Some are certain that The Beast of Revelation is the Roman Empire, Nero, the Pope, or someone else altogether.  The image of a beast arising from the sea first appears in Scripture at Isaiah 27:1. Leviathan is also mentioned earlier in the book of Job, but that reference may simply be from the animal kingdom.  However, Isaiah's reference surely points to a larger Spiritual oppressor, perhaps the very same being mentioned in Revelation 13:1.  Now, I am not suggesting that demons actually abode in the sea, but this Biblical metaphor illustrates an invisible, but very real, demonic landscape.  The tumultuous sea is used to picture the caustic habitat of demons.

In that day, Yahweh with his hard and great and strong sword will punish leviathan, the fleeing serpent, and leviathan the twisted serpent; and he will kill the dragon that is in the sea.

Isaiah 27:1 (WEB)

Now, consider an important concept.  The Revelation drama reveals illustrations of real people and interaction between the seen and unseen worlds.  I have also shown from Revelation 16:13-14, above, that demons are assigned various tasks in their great war against God and mankind.  The "frog" demons were sent to rally the kings of earth for war on the yet future Great Day of God.  Thus I propose that The First Beast is an actual demon chief alongside of Satan whose evil mission gave rise to the wicked Roman Empire.  His evil mission was accomplished through the wicked Roman Empire.  Thus he is portrayed with ten horns and seven heads illustrative of the Roman Emperors as explained in Revelation 13 and 17.  Yet because The Beast stands alongside Satan and is literally cast into the Lake of Fire with Satan, we know that he is also a demonic being.

Likewise for an early mention of a false demonic prophet we read,

20) A spirit came out, stood before Yahweh, and said, "I will entice him."  Yahweh said to him, "How?"  21) He said, "I will go, and will be a lying spirit in the mouth of all his prophets."  He said, "You will entice him, and will prevail also. Go and do so."  22) Now therefore, behold, Yahweh has put a lying spirit in the mouth of these your prophets; and Yahweh has spoken evil concerning you.

2 Chronicles 18:20-22 (WEB)

Perhaps, this deceiving spirit mentioned in the Old Testament, or another like him, is the demon called "The False Prophet" in Revelation 20.  Yet identifying the Second Beast with the demonic seems more problematic, at least initially.  The First Beast does not seem particularly human, but instead governmental, and so perhaps my proposal that a particular demon empowered Rome does not seem unreasonable.  However, the Second Beast instead seems to be more personal and human.  In fact, since the Second Beast gets his power from the First Beast he then seems like a human tyrant controlled by a demon, that is by the First Beast.  Common candidates for the Second Beast include Nero, Domitian, the Roman Concilia to enforce state worship, the Pope, and numerous others throughout history.

However, just like my proposal that the First Beast was a powerful demon whose work was manifest in the birth and growth of the Roman Empire, so I propose that the Second Beast was a powerful demon whose work was manifest in the wickedness of a Roman Emperor, perhaps Nero or Domitian.  Countless hours of effort have been spent in the effort to determine the identity of the Second Beast, The False Prophet, with the mysterious number of "666" given in Revelation 13:18 (WEB).

Here is wisdom. He who has understanding, let him calculate the number of the beast, for it is the number of a man. His number is six hundred sixty-six. 

The expression "number of a man" seems to indicate that "666" is the identity of a specific human being.  Some efforts at gematria identify Nero as the Second Beast, https://en.wikipedia.org/wiki/Number_of_the_Beast.  While this could easily be the case I also propose that Nero, or whoever the actual Second Beast proves to be, was specifically empowered by a demon.  Thus the Second Beast demon is finally damned to the Lake of Fire, not the human being he possessed.  Though one might question my concern to "save Nero," I am convinced he is saved by the same blood of Christ that saved you and me.  The expression above may also be better rendered "human numbering," meaning according to human calculation.  Consider that the mysterious number "666" is referenced at the end of a chapter discussing Satan, The Beast, and the False Prophet.  Certainly this triple "6" number must point to the terrible nature of demonic power that falls short of God's perfection in the Holy Trinity.  Since "7" is a picture of God's perfection and completeness, the number "666" may point to the climax of evil in the Unholy Trinity.  What worse scenario can you image than Satan working through a demonic government working through a demonic tyrant?

Revelation 20:10 then finally confirms that the demonic beings of Satan, The Beast, and The False Prophet are damned to the Lake of Fire for The Ages of The Ages.  God is not pronouncing doom to mere movements or governments.  How does one throw a movement into the Lake of Fire?  How does one torment a government for The Ages of The Ages?  Instead the only things ever mentioned as thrown into Hades or the Lake of Fire are people and places.  Further, it would seem curious for the Holy Spirit to explicitly highlight the damnation of Satan with one government and one government leader.  So, for my last point, the common destiny of the Unholy Trinity is likewise strong evidence for the common nature of these three beings.  This is especially so since Matthew 25:41 explicitly says that the Lake of Fire is "prepared for the Devil and his angels."

Read more about my understanding of Revelation in my articles in the Appendix, Eschatology is the Study of Future Good News! and Eschatology is the Study of Future Good News! (Part 2 with Grudem, Riddlebarger, Chilton, Summers, and Ewing).

Finally consider an extra-Biblical comparison.  Just as there are three demon leaders (Satan, the Beast, and the False Prophet), so God himself is three persons (God the Father, God the Son, and God the Holy Spirit).  The Bible does not highlight this parallel explicitly, but I mention it for you to ponder.  You or I might be tempted to think that the salvation and fate of mankind is uncertain and in question.  Too often my (and perhaps your) ministry efforts and actions reflect this uncertainty.  However, take a moment and fully rest in the grace of the Lord Jesus Christ.  Actually, you are advised to rest in the grace of the Lord Jesus Christ now and forever!  Our eternal destiny rests fully in his hands.  Our salvation is not uncertain!  Through his grace he does not consider us his enemies, but his chosen family -- redeemed for all eternity.

However, if we are not born again, our birth nature opposes God because our hearts are bad. We crucified Christ, but Christ loves and forgives us. Fallen angels also hate God, but God has promised to crush the head of Satan. Satan is the true enemy of God in this cosmic spiritual war.

Thus for the demonstration of his grace, God created angels and decreed that some would fall into rebellion and become his enemies destined for the Lake of Fire.  Why?  Perhaps to help us better understand grace, God decreed a dark frame to contrast his glorious mercy.  Apparently grace could not be fully praised and appreciated any other way.  The parallels between God's good nature and the evil nature of demons are noteworthy.  Consider a comparison of the Holy Trinity with the Unholy Trinity.

Friends, the salvation of mankind is not uncertain, nor is our salvation in question.  But sparks will fly until God throws his enemies (that is, Satan and the fallen angels that follow him) into the Lake of Fire for The Ages of The Ages.