If the natural result of war was famine, the natural result of famine is plague. The fourth horse is a sickly pale color, the color of death. The Greek χλωρός (chloros) is pale greenish gray (BDAG). Although the world is sometimes used for green grass or the flow of water, in medical texts the color is used in contrast to a healthy body, a “sallow” complexion (BrillDAG) or “typical of a corpse” (LN 79.35).
This is the only one of the four horsemen who is given a name: Death, and Hades following behind. Death is personified in Isaiah 25:8, for example. Hosea 13:14 refers to death and the grave as malevolent powers. In the Testament of Abraham16-20 personified Death comes to Abraham in the guise of youth and beauty.
Hades is the god of the underworld, the place of the dead. In the Septuagint, the word Hades is used to translate sheol, a Hebrew word meaning pit which is used for the place of the dead (Psalm 6:5, for example).
The four ways that Death is allowed to kill is drawn from Jeremiah and Ezekiel; this is a standard list of disasters which occurred when Jerusalem fell in 586 B.C. A similar list appears in 4Q171, and David Aune suggests Psalms of Solomon13:2-3, “The arm of the Lord saved us from the sword that passes through, from hunger and the death of sinners. Wicked beasts ran at them.” Dio Cassius describes the Second Jewish revolt in A. D. 135 using similar language (Aune 2:402).
Jeremiah 14:12 Although they fast, I will not listen to their cry; though they offer burnt offerings and grain offerings, I will not accept them. Instead, I will destroy them with the sword, famine and plague.”
Ezekiel 14:21 “For this is what the Sovereign LORD says: How much worse will it be when I send against Jerusalem my four dreadful judgments—sword and famine and wild beasts and plague—to kill its men and their animals!
4Q171 Col. i (frag. 1 line 26-27) Its [interpretation] concerns the Man of Lies who misdirected many with deceptive words, for they have chosen worthless things and did not lis[ten] to the Interpreter of Knowledge. This is why Col. II (frags. 1 II + 2 + 4Q183 3) they will die by the sword, by hunger and by plague.
Dio Cassius 69.1-2: Five hundred and eighty thousand men were slain in the various raids and battles [i.e., the sword], and the number of those that perished by famine, disease and fire was past finding out. Thus nearly the whole of Judaea was made desolate, a result of which the people had had forewarning before the war. For the tomb of Solomon, which the Jews regard as an object of veneration, fell to pieces of itself and collapsed, and many wolves and hyenas rushed howling into their cities.
Greg Beale suggests the four ways Death is given to kill humans is based on “the covenantal curse formulas of Lev. 26:18–28 and Deut. 32:24–26” (Revelation 383). He does not think there is a logical sequence from the first rider who is bent on conquest to the second (war), third (famine) and the fourth (pestilence). Although recognizing the curses do affect nations, they have “the dual purpose within the covenant community of purifying the faithful and punishing those disloyal to Christ” (384). For Beale, those slain by the plagues are “Christians as ‘slain’ and ‘killed’ (ἀποκτέννεσθαι) ‘because of the testimony that they held’” (386). This view does provide a neat segue into the fifth seal, the martyrs under the altar of God.
However, it seems best to see a general sequence of tribulation and persecution in the four horsemen, not unlike Jesus’s own words in the Olivet Discourse. In Matthew 24 Jesus describes a progression from international strife (wars and rumors of wars) to famine, earthquakes, persecution, and general apocalyptic events (eclipses of the sun and moon, falling stars, shaking of the “powers of heaven”). Revelation 6 follows this same pattern.