Onimi

Onimi was a male Yuuzhan Vong who lived during his species invasion of the Star Wars galaxy. A former member of the elite, he was condemned as a Shamed One when his attempt to graft Yammosk tissue onto his brain failed and left him deformed. A side effect of this was to restore the use of the Force to Onimi, which allowed him to take control of Shimrra Jamaane.

During the war Onimi was the true power behind the throne of the Yuuzhan Vong. Because of his Shamed One status he could not rule openly, so he had Shimrra take him on as a jester, whereby he could control the Supreme Overlord.

After the death of Shimrra Onimi decided that he would exterminate all life in the Star Wars galaxy. However he was defeated by Jacen Solo, who in a moment of total oneness with the Force was able to reverse all of Onimi's modifications and caused him to lose control of all the toxins Onimi was going to use against Solo. The toxins dissolved Onimi, causing the final Supreme Overlord of the Yuuzhan Vong to become a puddle of foul hydrocarbons which were absorbed by the floor of Shimrra's ship. The war would soon be over.

Trivia

 * Onimi's character was very similar to the Final Fantasy VI villain Kefka Palazzo and the Mario villain Dimentio. Both were seemingly just minions to the supposed main villains, yet were later revealed to be pulling the strings and (albeit indirectly, in the case of Onimi) betrayed the leaders to their deaths. Both also plotted mass-murder on a wide scale. In addition, it was implied that Onimi's insanity stemmed from the same event that gave him the ability to use the Force, similar to Kefka's insanity stemming from the procedure that led to him becoming the first Magitek Knight. Both also were killed with great cost to the main protagonist(s) (in Kefka's case, magic ended up vanishing from the world, with all Espers save for Terra dying with it. With Dimentio, Count Bleck and Tippi had to sacrifice themselves with a true marriage to seal away the Chaos Heart to ensure Dimentio was stopped after he was defeated. With Onimi, it was heavily implied that despite being defeated, he nonetheless managed to succeed in tipping the balance of the Force back to the Dark Side as well as beginning the sequence of events that led to Jacen Solo becoming a Sith Lord).