The Deep Fog is a supernatural fog that is a manifestation of the Old One's power and a primary antagonistic force in Demon's Souls - it is more akin to a force of nature than a villain but allows demons to enter the world and feed on human souls: the longer the Old One remains awake the greater the influence of the Deep Fog is on the land of mortals and the aim of the game is to lull the Old One back to sleep before the Deep Fog can engulf the entire world and doom humanity to a slow but steady extinction.