Palpatine

Emperor Sheev Palpatine (also known as Darth Sidious) is a fictional character and the main antagonist of the Star Wars saga. He is portrayed by Ian McDiarmid in the feature films. He was the Chancellor of the Galactic Republic and Senator of Naboo. He was killed by a redeemed Darth Vader when he tried to kill his son Luke Skywalker and fulfilled the Prophecy as the Chosen One.

Physical Appearance
Palpatine in the Original Trilogy is an aged, pale-faced figure who wears dark robes. In the Prequel Trilogy, he looks like a kindly old man. He gains the aforementioned appearance in the Original Trilogy as a result of his own Force Lightning being redirected back at him by Mace Windu in their duel in the Chancellor's office on Coruscant in Revenge of the Sith. However, it's also implied in other sources that Palpatine's disfigured appearance was in fact his true appearance caused by decades of usage of the Dark Side of the Force and that his affable appearance was the result of a specialized form of alchemy known aptly as Mask.

Personality
In the films and the Expanded Universe, Palpatine is portrayed as cunning and deceptive in manipulating people and events to achieve his goals. Palpatine's principal desire is to have ultimate power. Palpatine presents himself in public to others as a modest, polite, as well as harmless person. However behind this public persona, in reality he is an arrogant, ruthless, cruel, sadistic, Machiavellian megalomaniac, psychopath and misanthropist.

Abilities
He possessed several Force abilities, due to his being a Sith Lord. Two of which were demonstrated in the movies: He could summon Force Lightning to torture and/or kill his opponents and he also utilized telekinesis, either as an offensive attack or simply as a means of displaying his power, the latter being most prevalent when he used the ability to remove Luke Skywalker's binders aboard the Death Star II while barely lifting a finger. He was also strongly implied to be one of, if not the most powerful Sith to have existed. He was also incredibly skilled at using lightsabers.

Star Wars Episode V: The Empire Strikes Back
Palpatine first appeared as the unnamed Emperor of the Galactic Empire in the 1980 film The Empire Strikes Back and was voiced by Clive Revill (later portrayed by Ian McDiarmid in the later Special Edition releases). In the film he contacts Darth Vader via holographic communication and tells him of a "great Disturbance in the Force," and warns him that Luke Skywalker is becoming a threat. But Vader convinces the Emperor that Luke would be an asset if he could be turned to the dark side of the Force.

Star Wars Episode VI: Return of the Jedi
In Return of the Jedi, Palpatine (now portrayed by Ian McDiarmid) arrives on the second Death Star to oversee the final stages of the war between the Rebel Alliance. When Vader delivers his son, to Palpatine, the Emperor—intent on replacing Vader with a younger, more powerful apprentice—tempts the young Jedi to the dark side by appealing to his fear for his friends. This leads to a lightsaber duel in which Luke defeats and nearly kills Vader. Luke ultimately refuses to turn to the dark side, which angers Palpatine who attacks him with Force Lightning and ignoring the shield generator protecting the Death Star II been destroyed by the Rebel strike team allowing Lando Calrissian and Wedge Antilles to prepare to attack it. Vader, witnessing the suffering of his son, turns on his master who was really the true traitor and enemy of the Galactic Republic that Mace Windu warned him in the Clone Wars and redeems himself by throwing the evil Emperor into the Death Star's reactor shaft to his death and fulfilled the Prophecy as the Chosen One.

Prequel trilogy
In the prequel trilogy, Palpatine is a middle-aged politician of the Republic who rises to power through deception and treachery. As the Senator from Naboo and later the Chancellor of the Republic, he outwardly behaves like a well-intentioned and loyal public servant and supporter of democracy, yet underneath his affable public persona lurks his true identity: Darth Sidious, a Dark Lord of the Sith. As both Palpatine and Sidious, he sets into motion a series of events—including the Clone Wars—which ultimately destroys the Jedi Knights and the Republic, allowing him to usher in the Galactic Empire, a brutal authoritarian regime.

Ian McDiarmid has hinted at the possibility of reprising the role for the sequel trilogy.

Star Wars Rebels
In the first season Palpatine makes a brief appearance on the Holonet broadcast in the episode "Empire Day" but is expected to appear in the second season and will be voiced by Sam Witwer, who originally provided both the voices of Emperor Palpatine and Galen Marek/Starkiller (Darth Vader's apprentice) in the 2008 video game Star Wars: The Force Unleashed and the 2010 sequel Star Wars: The Force Unleashed II.

Star Wars Weekends
He was a meetable character during the Star Wars Weekends event in Disney's Hollywood Studios at The Walt Disney World Resort.

Trivia

 * Since the initial theatrical run of Return of the Jedi, Palpatine has become a symbol of evil and sinister deception in popular culture. People have compared his corrupt leadership to many dictators throughout history and his appearance to that of Benedict Arnold.
 * The film historian Robin Wood has compared Palpatine's appearance to that of the Evil Queen's witch form in Snow White and the Seven Dwarfs. Coincidentally, both of their disfigured appearances had some relation to lightning that they summoned (the Queen added lightning to a potion as part of an ingredient to fashion a disguise for herself and Palpatine's body ended up disfigured as a direct result of Mace Windu redirecting his Force Lightning back at Palpatine when he attempted to blast him with it, although it was heavily implied with the latter that the disfigurements were actually his true form being exposed).
 * Contrary to popular belief, Palpatine was not referred to by name until The Phantom Menace. His name originated from supplementary materials such as the visual dictionary for the original trilogy, the script, and the novelizations.
 * Palpatine's defeat and later death at the hands of Vader was referenced in Toy Story 3, where Big Baby picked up Lotso after one abuse too many and threw him in the dumpster. At the time the movie was released, Disney had not acquired the rights to Star Wars yet.