Tragedy of Darth Plagueis the Wise (Earth-2356)

"Did you ever hear the Tragedy of Darth Plagueis the Wise? No. I thought not. It's not a story the Jedi would tell you. It's a Sith legend."

- Sheev Palpatine and Anakin Skywalker

The "Tragedy of Darth Plagueis the Wise" was a so-called "Sith legend" that recounted the murder of Darth Plagueis by the hand of his own apprentice, Darth Sidious. Plagueis, the legend went, was "so powerful and so wise he achieved what no only the Sage of Six Paths could do so thousands of years in the past: using forbbiden techniques, he could channel the Force to influence the midi-chlorians to create life," and even save others from dying. "He became so powerful, the only thing that he was afraid of was losing his power. His apprentice, Sidious, killed him in his sleep."

Towards the end of the Clone Wars, Supreme Chancellor Sheev Palpatine recounted that tale to Anakin Skywalker on his private box at the Galaxies Opera House in hopes of luring him to the dark side of the Force. In fact, Palpatine was none other than the public persona of Darth Sidious, and he only framed the tale of Plagueis' murder as an old legend so as to avoid suspicion.

According to Palpatine, what made it a tragedy was that he could not save himself from death, despite being able to save others. When Palpatine told this story to Skywalker, Skywalker countered that it was only a tragedy for Plagueis, and for the apprentice it was a happy ending. Palpatine later revealed that he was the unnamed apprentice, and that Plagueis' ability had been real; this was one of the steps towards turning Skywalker to the dark side of the Force.

Source

 * https://starwars.fandom.com/wiki/The_Tragedy_of_Darth_Plagueis_the_Wise.
 * https://starwars.fandom.com/wiki/Tragedy_of_Darth_Plagueis.