Darth Plagueis (Earth-2017)

"Darth Plagueis was a Dark Lord of the Sith so powerful and so wise, he could use the Force to create life. He had such a knowledge of the dark side, he could even keep the ones he cared about from dying. He became so powerful, the only thing he was afraid of was losing his power...which, eventually of course, he did. Unfortunately, he taught his apprentice everything he knew. Then his apprentice killed him in his sleep. Ironic. He could save others from death...but not himself."

- - Chancellor Snoke Palpatine

Darth Plagueis was a Dark Lord of the Sith and the master of Darth Sidious. He was so powerful with the Force that he managed to discover immortality. However, he was betrayed by his apprentice as per the Rule of Two. Sidious, attending as Chancellor Snoke Palpatine, recounted the events of his rise and fall to manipulate Galen Marek into the dark side.