"And He broke the forth seal, I heard the voice of the forth living creature saying, 'Come.' And I looked, and behold, an ashen horse; and he who sat on it had the name Death; and Hades was following with him. And authority was given to them over a forth of the earth, to kill with sword and with famine and with pestilence (or death) and by the wild beasts of the earth." (Rev. 6:7, 8 NASB).
Ashen is a sickly pale color, the "color" of death. Whether a quarter of the earth is meant geographically, or a quarter percentage of the entire population, is not yet known. "Wild beasts" is not literally wild animals gone berserk. It's symbolic of unscrupulous, bestial men following the dictates of barbarous nature, without conscience. This could involve the hunting down and persecution of the church and/or Israel (c.f., Matt. 24:9-14).