Samuel Fate is the ruler of a vast inter-stellar empire that threatens the world of the Course Books, who first appears in The Inclination to Destiny and becomes the chief antagonist. Originator of the Long Night; destroyed in the New Day.
Absolutely nothing is known about Samuel Fate and very little is given about his empire. He is a mage of unspeakable power, and commands an army that wields both magic and technology. He is known by Laytami Gudersnipe and identified rather cryptically as "the one we missed". This eludes to the idea that he, or his ancestors, escaped destruction at the end of the Mage Wars, and originated from the Dynastic era. (Some cultists believe him to be a descendant, or successor, of Joseph Manse; but the Foundation dismissed this hypothesis, on grounds that Manse and all his most capable followers, died with their campaign in the Sixth Age).
Various characters throughout the canon refer to areas of the Multi-Verse in which "the Mage Wars never stopped", and it is hinted that Fate and his empire may be only one of dozens like it, in such places. However, victory over Samuel Fate appears to be the one thing necessary to secure the continued existence of the world as we know it.
Samuel Fate's orgin may be shrouded in deep antiquity. He commands a vast empire in a region beyond the Known Worlds, and seems to have even been unconnected with the Eladamri and the Roads War. While his age is unknown, his region likely became seperated from the known worlds during the Mythical Age at the Breaking of the World.
The exact size of Fate's empire is not given, but it is generally indicated to be vast. He is able to conquer the entirety of the known worlds within the span of a few human generations (a remarkable feat, considering that without GATE travel it would take at least that long just to move from one side to the other).
Samuel Fate rules primarily by peddling in ignorance. Some worlds are allowed to maintain high levels of technology in order to manufacture war goods, but most of the population is forced to technologically regress. Fate employs technologies similar to the Origin Satellite on technologically advanced worlds to meet this goal. His fleet arrives in the Known Worlds aboard Allusion Warships.
Much like the Kamians, Fate has little use for worlds that cannot serve him in some major way: either industrially (by providing labor), or technologically. Those that can do neither are blasted back to pre-industrial levels and kept there, where Fate is installed as a god.