Fury of the Immortals
The Immortals are vastly powerful and act as gods or demi-gods taking an interest the affairs of mortals. They themselves draw their power from the Spheres of Power, but their power is also derived from the strength and devotion of their followers. In many cases, the Immortals are national patrons or heroes whom followers have dedicated themselves to emulating. They will often compete with the patrons of other nations to advance the interests of their nation. While strictly forbidden from directly interfering in mortal affairs, they are known to influence Mystaran events through their followers, clerics and agents. They have also been known to assume mortal form and walk Mystara in disguise.
None but the Immortals know the origins of these powerful beings, but many Immortals, particularly those that patronize specific nations, may have begun existence as mortal beings.