Death? On a pale horse?
Fourth Seal: A pale horse appears, whose rider is Death, and Hades follows him. Death is granted a fourth part of the earth, to kill with sword, with hunger, with death, and with the beasts of the earth. (6:7–8)
Thank you all for the suggestions -- I was thinking of Death as the fourth horseman, but though we have Famine at 14A, War at 20A and Pestilence at 26A, I don't see Death, or a synonym for it, anywhere. Maybe only the first three were intended to be in the puzzle (because mentioning d---- is taboo)!