2. Darth Plagueis The Wise
Though he was mentioned in Episode III, one of the most powerful Sith lords in history has yet to make an appearance in any Star Wars film. Dath Plagueis was a Muun Dark Lord of the Sith and was Master to Darth Sidious, a.k.a. Palpatine. Plagueis taught Palpatine about the Dark side of the Force and the ways of the Sith. Together, they came up with a plan for Sidious to take control over the Galaxy, bringing in a new era of Sith dominance. It is also highly likely that their manipulating the Force energy in the Galaxy indirectly led to the midichlorians conceiving Anakin Skywalker. Of course, Sidious proved to be more devious than his Master thought; Plagueis was planning on becoming Supreme Chancellor himself, while Palpatine planned to take that role for himself. The night before Palpatine was elected Supreme Chancellor, he betrayed and murdered his Master. With Plagueis dead, Sidious was able to find himself a new apprentice, and since Maul was killed around the same time, he was free to begin manipulating Skywalker to his cause. Plagueiss contributions to the Star Wars universe were very important, because he was central in the creation of the most diabolically evil antagonist in the entire franchise. Without Plagueis, Palpatine might not have learned about the Force, or how it can be used to manipulate life. This particular ability was central to Anakin Skywalkers fall from grace, and Palpatine cleverly used this to his advantage.