Emperor Palpatine/Darth Sidious

Palpatine, also known as Darth Sidious and the Emperor, was the main antagonist of the Star Wars franchise, serving as the main antagonist of Star Wars: Episode 1 - The Phantom Menace, a major antagonist in Star Wars: Episode 2 - Attack of the Clones, the main antagonist of Star Wars: Episode 3 - Revenge of the Sith, a minor antagonist in Star Wars: Episode 5 - The Empire Strikes Back, and the main antagonist of Star Wars: Episode 6 - Return of the Jedi. He was Luke's arch-nemesis and Darth Vader's former leader and boss.

Prequel trilogy
In the 1999 prequel Star Wars: Episode I – The Phantom Menace, which is set 32 years before Star Wars, Palpatine is depicted as a middle-aged Galactic Senator from the planet Naboo who is secretly the Sith Lord Darth Sidious. As Sidious, he influences the corrupt Trade Federation to blockade and invade Naboo. Queen Padmé Amidala of Naboo flees to the planet Coruscant to receive counsel from Palpatine, unaware that he actually engineered the invasion. After a plea for help from the senate results in bureaucratic delays, Palpatine persuades the queen to make a motion to have Supreme Chancellor Finis Valorum removed from office.

When Padmé attempts to liberate Naboo, Sidious sends his Sith apprentice Darth Maul there to capture her. The invasion is eventually thwarted and Maul is defeated in a lightsaber duel with Obi-Wan Kenobi. Palpatine uses the crisis to be elected the new Chancellor of the Republic. He then returns to Naboo, where he befriends the young Anakin Skywalker, telling him that, "We will watch your career with great interest".

In the 2002 sequel Star Wars: Episode II – Attack of the Clones, Palpatine exploits constitutional loopholes to remain in office even after the official expiration of his term. Meanwhile, as Darth Sidious, he continues to manipulate events from behind the scenes by having his new Sith apprentice Count Dooku, a former Jedi master, lead a movement of planets in seceding from the Republic to form the Confederacy of Independent Systems.

Since the Separatists are secretly building a battle droid army, Palpatine uses the situation to have himself granted emergency powers. Palpatine feigns reluctance to accept this authority, promising to return it to the Senate once the crisis has ended. His first act is to allow the creation of a clone army to counter the Separatist threat; this results in the opening salvo of the Clone Wars. With the galaxy now at war as Sidious planned, Dooku brings him the secret plans for a new superweapon.

The Clone Wars (2008)
In the 2008 animated film Star Wars: The Clone Wars (also set between Attack of the Clones and Revenge of the Sith), Darth Sidious engineers a Separatist plot where Count Dooku turns Jabba the Hutt against the Republic by kidnapping his son Rotta and framing the Jedi for it. Meanwhile, Palpatine suggests that the Republic ally itself with the Hutts. Although Anakin Skywalker and his Padawan Ahsoka Tano foil the plot, the outcome suits Palpatine's ends: Jabba places Hutt hyperspace routes at the Republic's disposal.

Revenge of the Sith
In the 2005 sequel Star Wars: Episode III – Revenge of the Sith, Palpatine is captured by cyborg Separatist general General Grievous, as part of a plan devised by Sidious. Palpatine is rescued by Anakin and Obi-Wan, but not before the Jedi confront Count Dooku again. A duel ensues in which Anakin defeats Dooku. Palpatine orders Anakin to kill the unarmed Dooku; after some hesitance, Anakin kills Dooku in cold blood. Palpatine then escapes with his Jedi rescuers and returns to Coruscant. By this point, Palpatine has become a virtual dictator, able to take any action in the Senate. He makes Anakin his personal representative on the Jedi Council, who deny Anakin the rank of Jedi master and order him to spy on the Chancellor. Palpatine tells Anakin the story of Darth Plagueis, a powerful Sith Lord who was able to manipulate life and death but was killed by his own apprentice. Eventually, Palpatine reveals his secret identity as a Sith Lord to Anakin; he knows that Anakin has been having prophetic visions of Padmé, his pregnant secret wife, dying in childbirth, and offers to teach him Plagueis' secrets to save her life.

Anakin informs Jedi Master Mace Windu of Palpatine's treachery. With three other Jedi masters at his side, Windu attempts to arrest Palpatine, but Palpatine produces a lightsaber from his sleeve and quickly dispatches all but Windu. Palpatine engages Windu in a duel and fires Force lightning at him, but Windu deflects the lightning back at its source, deforming Palpatine's face into the gray, wizened visage seen in the original trilogy. Just as Windu is about to dispatch Palpatine, Anakin appears and intervenes on the Sith lord's behalf, allowing Palpatine to kill Windu with another blast of lightning. Anakin then pledges himself to the dark side as Palpatine's new Sith apprentice, Darth Vader.

Palpatine orders the clone troopers to turn on their Jedi generals, while dispatching Vader to kill everyone inside the Jedi Temple and then murder the Separatist leaders on the planet Mustafar. Palpatine then reorganizes the Republic into the Galactic Empire, with himself as Emperor. Jedi Master Yoda confronts him in his Senate office and engages the Sith Lord in a lightsaber duel that ends in a stalemate. Sensing that his new apprentice is in danger, Palpatine travels to Mustafar and finds Vader near death following a duel with Obi-Wan. After returning to Coruscant, he rebuilds Vader's burned, mutilated body with the black armored suit from the original trilogy. Palpatine then tells Vader that Padmé was killed in the heat of Vader's anger, breaking what remains of his apprentice's spirit. Palpatine is last seen watching the original Death Star's construction, with Vader and Wilhuff Tarkin at his side.

Original trilogy
The Emperor is briefly mentioned in the original Star Wars, the first film in the original trilogy. Grand Moff Tarkin explains to his fellow Imperials that the Emperor has dissolved the Senate.

The Emperor first appeared as a major antagonist in The Empire Strikes Back. He appears in hologram form to address Darth Vader, his Sith apprentice. He tells Vader that Luke Skywalker is becoming a serious threat to the Empire and must not become a Jedi. Vader convinces him that Luke would be a great asset if turned to the dark side.

In 1983's Return of the Jedi, the Emperor appears in person to oversee the last stages of the second Death Star's construction. He is the film's main antagonist and assures Darth Vader that they will together turn Luke, now revealed to be Vader's son, to the dark side. Unknown to Vader, the Emperor plans to replace his apprentice with Luke. When Vader brings Luke before his master, the Emperor tempts Luke to join the dark side by appealing to the young Jedi's fear for his friends, whom he has lured into a trap. This leads to a lightsaber duel in which Luke defeats and nearly kills Vader. The Emperor tells Luke to kill Vader and take his place, but Luke refuses and declares himself a Jedi. Enraged, the Emperor attacks Luke with Force lightning. Moved by his son's cries for help, Vader throws the Emperor into the Death Star's reactor shaft, killing him.