Star Wars: The Sith'ari Prophecy a.k.a the Sith Prophecy

Sith'ari was a title that, in the ancient Sith, meant "Lord" or "Overlord," first claimed by King Adas. After Adas's death, the term became the subject of a legend prophesying the coming of a being that would lead and destroy the Sith, but in doing so would make the Sith more powerful than ever before. In this context, the term came to mean "perfect being" or "god."^[1]The prophecy, which was in many ways similar to the Jedi prophecy of the Chosen One,^[1]retained its significance for the Dark Lords^[2] up until the time of the Order of the Sith. 
Source: http://starwars.wikia.com/wiki/Sith%27ari