Sheev Palpatine (/ˈpælpətiːn/ PAL-pə-teen) is the main antagonist of the Star Wars franchise. He first appeared in the 1980 film The Empire Strikes Back as the Emperor. He is also known by his Sith name, Darth Sidious, which was first used in the novelization of the 1999 film The Phantom Menace.

Palpatine appears in all three film trilogies in the Skywalker Saga, and is portrayed by Ian McDiarmid in all five films in which he physically appears. In the original trilogy, Palpatine is Emperor of the Galactic Empire and the master of Darth Vader. In the prequel trilogy, which chronicles his rise to emperor, Palpatine is a senator from the planet Naboo who plots to become Supreme Chancellor of the Galactic Republic. He masterminds the Clone Wars to turn the Republic into the Empire, destroys the Jedi Order, and manipulates Anakin Skywalker into becoming his apprentice, Darth Vader. In The Rise of Skywalker (2019), the final film in the sequel trilogy, a resurrected Palpatine is revealed to be the grandfather of Rey, a Jedi-in-training who is the protagonist of the sequel trilogy. He is also the mastermind behind Snoke, whom he created to lead the First Order against the New Republic and seduce Skywalker's grandson, Ben Solo, into becoming Kylo Ren.

Palpatine's story was inspired by real-world examples of political strongmen and democratic backsliding during the rise and rule of dictators such as Julius Caesar, Napoleon Bonaparte, and Adolf Hitler. Since the release of the original trilogy, Palpatine has become a widely recognized symbol of evil in popular culture. Since the prequel trilogy, he has been a symbol of sinister deception and the subversion of democracy. In addition to the films, Palpatine appears in the series Clone Wars, The Clone Wars, Star Wars Rebels, The Bad Batch, Obi-Wan Kenobi and Star Wars: Tales. He also appears in Star Wars novels and comics.

George Lucas created the Star Wars franchise and the character Palpatine. His conceptualization of Palpatine and the role he plays in the franchise changed over time. Lucas's initial notes discuss a line of corrupt emperors, not just one. In the 1974 draft of Star Wars, the "New Galactic Empire" was led by a relatively young human named Cos Dashit. The name Palpatine first appears in the prologue of Alan Dean Foster's 1976 novelization of Star Wars, which details the Emperor's rise to power. From Return of the Jedi (1983) onwards, the Emperor became the ultimate personification of evil in the series. Though the films of the original Star Wars trilogy do not actually state the Emperor's name, the novelization of Return of the Jedi states his surname as Palpatine. He was given the first name Sheev in the 2014 novel Tarkin.

During the story development of The Empire Strikes Back (1980), Lucas decided that, with the original having only passingly mentioned the Emperor, he needed to "begin to deal with him on a more concrete level". Lucas realized, however, that the primary conflict with the Emperor would be best saved for the trilogy's third film, Return of the Jedi, because "[w]hen you get rid of the Emperor, the whole thing is over." Discussing the character's importance to the story, Lucas stated that "In the end, the Emperor does exactly what [Obi-Wan Kenobi] did; he can also transform himself", referring to the ability to live after death through the Force. Although Palpatine dies at the end of Return of the Jedi, the plot point of his metamorphosis was utilized for the sequel trilogy, which Lucas had no direct involvement with.

In Return of the Jedi, the initial conception of Palpatine as a weak, isolated figurehead was superseded by his depiction as a dictatorial ruler adept in the dark side of the Force. The Emperor was inspired by the villain Ming the Merciless from the Flash Gordon comic books. The characterization of Palpatine as a ruthless politician dismantling a democratic republic to achieve supreme power was in part inspired by the real-world examples of democratic backsliding during the rise and rule of Julius Caesar, Napoleon Bonaparte, Alberto Fujimori, Ferdinand Marcos Sr., and Adolf Hitler. Other elements of the character come from Richard Nixon. Lucas said that Nixon's presidency "got me to thinking historically about how do democracies get turned into dictatorships. Because the democracies aren't overthrown; they're given away." Lucas also said, "The whole point of the movies, the underlying element that makes the movies work, is that you, whether you go backwards or forwards, you start out in a democracy, and democracy turns into a dictatorship, and then the rebels make it back into a democracy."

Lucas wanted to establish the Emperor as the true source of evil in Star Wars. Screenwriter Lawrence Kasdan noted, "My sense of the relationship between Darth Vader and the Emperor is that the Emperor is much more powerful ... and that Vader is very much intimidated by him. Vader has dignity, but the Emperor in Jedi really has all the power." He explained that the climax of the film is a confrontation between Vader and his master. In the first scene that shows the Emperor, he arrives at the Death Star and is greeted by a host of stormtroopers, technicians, and other personnel. Lucas states he wanted it to look like the military parades on "May Day in Russia."

Lucas fleshed out the Emperor in the prequel trilogy. According to Lucas, Palpatine's role in The Phantom Menace is to explain "how Anakin Skywalker [later Vader] came to be Palpatine's apprentice" and the events that sparked Palpatine's rise to totalitarian power after being a senate representative. The film's novelization is the first time he is called Darth Sidious. His home world, Naboo, is also home to Anakin's romantic interest, Padmé Amidala, who later becomes a senator of that planet.