The Tragedy of Darth Plagueis "The Wise" is a copypasta originating from Star Wars Episode III: Revenge of the Sith. It has gained popularity online as a meme among Star Wars fans.
In Star Wars Episode III: Revenge of the Sith, Chancellor Palpatine, secretly Darth Sidious, tells Anakin Skywalker a legend to to lure him further to the dark side of the force, as Anakin was having visions of his wife, Pé Amidala, dying in childbirth. The legend is about a Dark Lord of the Sith, Darth Plaguies The Wise, who could influence midichlorions to prevent people from dying. However, he taught his apprentice all he knew, and then the apprentice killed him while he was asleep. Palpatine finds the legend ironic, because while Darth Plaguies could save others from death, he could not save himself.