"When the Lamb broke the fourth seal, I heard the voice of the fourth living creature saying, “Come.” I looked, and behold, an ashen horse; and he who sat on it had the name Death; and Hades was following with him. Authority was given to them over a fourth of the earth, to kill with sword and with famine and with pestilence and by the wild beasts of the earth."
Death is one of the four Horsemen of the Apocalypse, and is to ride the gray horse during the End of Days. He guides the souls of the dead to the afterlife, whether that destination be Heaven or Hell. He has a strained relationship with Heaven and an even worse relationship with Satan and his underlings. The Fallen's sporadic contracting aggravates Death because it alters the length of a soul's time on Earth, rendering the time of reaping and final destination of the soul unpredictable.