Revelation 6:7-8

7When He (the Lamb) broke open the fourth seal, I heard the voice of the fourth living creature call out, “Come.”

8So I looked, and behold, an ashen (pale greenish gray) horse [like a corpse, representing death and pestilence]; and its rider’s name was Death; and Hades (the realm of the dead) was following with him. They were given authority and power over a fourth part of the earth, to kill with the sword and with famine and with plague (pestilence, disease) and by the wild beasts of the earth.