Palpatine, also known as Darth Sidious, was the last Chancellor of the Galactic Republic and the first Emperor of the Galactic Empire. He was known to be the most powerful Sith Lord who ever existed and he followed Darth Bane's Rule of Two. Before that time, he was trained by a Muun Sith Lord named Darth Plagueis. Palpatine was able to establish his Empire by concocting a complex master plan, which involved starting the Clone Wars, a galaxy-wide conflict that cost billions of sentient lives. Palpatine himself headed both the Galactic Republic and, secretly, the Confederacy of Independent Systems, which allowed him to prolong the conflict in order to gain more executive powers from the Senate.
When his power as Chancellor had reached its dictatorial peak, Palpatine abolished the Republic and replaced it with the first Galactic Empire with himself as leader. With the Imperialization of the galaxy, Emperor Palpatine effectively had total control over its people, and was able to create one of the most powerful military forces the galaxy had ever seen. For nineteen years, Palpatine's rule would go relatively unopposed, until disgruntled former Imperial senators founded the Alliance to Restore the Republic. The Galactic Civil War would last for many years, but in 4 ABY, he was killed by Darth Vader, his former Sith apprentice who redeemed himself as the Chosen One, during the Battle of Endor. However, this did not mean the end of the Empire.