Second Foundation
The Mule's conquest is amazingly fast: he defeats the Foundation and establishes the Union of Worlds after only five years. Then, just as suddenly, and seemingly randomly, he stops his advance and settles into a five-year period of consolidation. This is actually because the Mule fears the mysterious Second Foundation, which is rumored to be capable of defeating a mentalic person like himself. According to a hint given by Hari Seldon, the Second Foundation was founded at "the opposite end of the galaxy" from the First Foundation, which was itself founded on the distant galactic rim planet Terminus. However, the true location of the Second Foundation is a mystery and popular sentiment is that it does not exist. Nevertheless, in anxiety the Mule launches repeated expeditions in search of the Second Foundation during this period of consolidation.