...a white horse: and he that sat on him...

This is the angel of natural death.  The bow symbolizes the bow of Apollo or Artemis, bringers of death in the ancient religion of Greece and Rome. He is given a crown and goes forth conquering, and to conquer because he is instituted as master over all the living until the end of time. Until that time, none shall escape him, except by falling to the hands of another form of death. He emerges first because this was the first form of death that came into the world, through the sin of Adam and Eve, as St. Paul wrote, "Through one man sin entered into the world, and through sin, death; and thus death has passed unto all men" (Romans 5:12).