Darth Plagueis also known as Darth Plagueis the Wise was one of the most powerful Sith Lords in history. Darth Plagueis was so strong in the dark side of the force that he could even use it to stop those he loved from dying. Darth Plagueis was trained by Darth Bane and when Plagueis was done with his Master's training he killed him and later went on to train a young boy from Naboo called Palpatine who would later rise to become Darth Sidious.
Darth Plagueis was obsessed with eternal life and eventually found a way to use the Dark side to cheat death. However Plagueis's powers of cheating death would only work for others, and one fateful night his apprentice Sidious killed him in his sleep.
Sidious often tried to mimic Plagueis power of cheating death and gaining eternal life but he always failed.