Who are the four horsemen of the Apocalypse?
The four horsemen are the riders of the white, red, black, and pale horses revealed when the Lamb opens the first four seals in Revelation 6; they are real angelic beings sent by God, not symbols of nations or the devil, and their identity is clarified by the four spirits of heaven in Zechariah.
The four horsemen of the Apocalypse appear when the Lamb opens the first four seals of the scroll in Revelation 6. The first seal reveals a white horse whose rider has a bow and is given a crown, going forth conquering and to conquer. This rider is understood as a conquering figure connected to deception, conquering through false religion, false doctrines, and gross deceptions, a judgment on those who reject the truth of the Gospel even though they know it in their hearts. The second seal brings forth a red horse whose rider is given a great sword and power to take peace from the earth, causing men to kill one another, bringing violence and war. The third seal reveals a black horse whose rider holds a pair of balances, bringing famine and economic hardship, so that a measure of wheat costs a penny while the oil and wine are protected from the scarcity. The fourth seal reveals a pale horse whose rider is named Death, with Hell following after him, and together they are given power over a fourth part of the earth to kill by sword, hunger, death, and wild beasts.
These four horsemen are not symbols invented within Revelation itself, nor are they devils or earthly nations as many suppose. Because Revelation never explains the horses directly, the book of Zechariah is used to shed light on who they are. Zechariah 1:8 to 11 describes a man on a red horse among horses of red, speckled, and white, who are identified as those whom the Lord has sent to walk to and fro through the earth. Zechariah 6:1 to 8 describes four chariots with red, black, white, and grisled (pale) horses, which the angel explains are the four spirits of the heavens that go forth from standing before the Lord of all the earth. This shows that the four horsemen are angelic spirits in God's service, not devils and not nations, and that they have been walking to and fro through the earth long before the seals of Revelation were opened, meaning they were already active in the world and the seals simply reveal their ongoing function.
Because the appointment of rulers and the unfolding of judgments belong to God rather than to human wars or elections, Daniel 4:17 and 4:35 are cited to show that the Most High rules in the kingdoms of men and gives them to whomever He chooses, and that none can stay His hand. This means that even when the antichrist rises and terribly subdues the earth, whatever he does must first be allowed by these four horses and their riders, so the antichrist is used as a pawn to fulfill God's will rather than acting independently.
The seals themselves are described as previews or a table of contents for the judgments written within the sealed scroll, not as the cause of the events. The four horsemen have their judgments unfold more fully later in the Trumpet and Vial judgments; for example, the pale horse rider named Death and Hell is later shown releasing the stinging locusts and the two hundred million army of Revelation 9, since Jesus holds the keys of hell and death and gives this rider the authority to loose them upon the earth.
The scriptures
And I saw when the Lamb opened one of the seals, and I heard, as it were the noise of thunder, one of the four beasts saying, Come and see. And I saw, and behold a white horse: and he that sat on him had a bow; and a crown was given unto him: and he went forth conquering, and to conquer.
And when he had opened the second seal, I heard the second beast say, Come and see. And there went out another horse that was red: and power was given to him that sat thereon to take peace from the earth, and that they should kill one another: and there was given unto him a great sword.
And when he had opened the third seal, I heard the third beast say, Come and see. And I beheld, and lo a black horse; and he that sat on him had a pair of balances in his hand. And I heard a voice in the midst of the four beasts say, A measure of wheat for a penny, and three measures of barley for a penny; and see thou hurt not the oil and the wine.
And when he had opened the fourth seal, I heard the voice of the fourth beast say, Come and see. And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.
I saw by night, and behold a man riding upon a red horse, and he stood among the myrtle trees that were in the bottom; and behind him were there red horses, speckled, and white. Then said I, O my lord, what are these? And the angel that talked with me said unto me, I will shew thee what these be. And the man that stood among the myrtle trees answered and said, These are they whom the LORD hath sent to walk to and fro through the earth. And they answered the angel of the LORD that stood among the myrtle trees, and said, We have walked to and fro through the earth, and, behold, all the earth sitteth still, and is at rest.
And I turned, and lifted up mine eyes, and looked, and, behold, there came four chariots out from between two mountains; and the mountains were mountains of brass. In the first chariot were red horses; and in the second chariot black horses; And in the third chariot white horses; and in the fourth chariot grisled and bay horses. Then I answered and said unto the angel that talked with me, What are these, my lord? And the angel answered and said unto me, These are the four spirits of the heavens, which go forth from standing before the LORD of all the earth. The black horses which are therein go forth into the north country; and the white go forth after them; and the grisled go forth toward the south country. And the bay went forth, and sought to go that they might walk to and fro through the earth: and he said, Get you hence, walk to and fro through the earth. So they walked to and fro through the earth. Then cried he upon me, and spake unto me, saying, Behold, these that go toward the north country have quieted my spirit in the north country.
This matter is by the decree of the watchers, and the demand by the word of the holy ones: to the intent that the living may know that the most High ruleth in the kingdom of men, and giveth it to whomsoever he will, and setteth up over it the basest of men.
And all the inhabitants of the earth are reputed as nothing: and he doeth according to his will in the army of heaven, and among the inhabitants of the earth: and none can stay his hand, or say unto him, What doest thou?
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.