Rule of Two

"Two there should be. No more, no less. One to embody power, the other to crave it."

- Darth Bane

The Rule of Two was a Sith philosophy mandating that only two Sith Lords could exist at any given time: a master to embody the power of the dark side of the Force, and an apprentice to crave it. The philosophy of two governed the Lords of the Sith for a millennium, beginning with its founder Darth Bane.

Creation
"Created the Rule of Two, you did."

- Yoda, to the specter of Darth Bane

Even before Darth Bane created the rule, the Sith doctrines still rotated somewhat around the idea of two: a master and an apprentice. Some Sith temples could only be entered by a pair of Force-users.

Eventually, Darth Bane became the sole survivor of a war against the Jedi Order a millennium before the Clone Wars. Recognizing that it was Sith greed and in-fighting that led to their destruction, Bane created the Rule of Two so the Sith could operate in secret, using subterfuge to plot their revenge against the Jedi. Bane developed the philosophy after his personal experiences and by studying ancient Sith documents.

Bane took an apprentice of his own and passed on his knowledge while establishing the new Sith way of pursuing power and revenge against the Jedi through manipulation and subterfuge. The Jedi became aware of Bane's philosophy and Bane was defeated. Although historical records weren't accurate, it was considered possible that Bane was killed by his own apprentice. Anyway, the Jedi went to falsely believe that they had destroyed the Sith forever. However, Bane's plans continued through his apprentice, allowing the Sith to survive secretly for years while planning their revenge against the Jedi Order.

Plagueis and Sidious
The Sith carried out their vendetta for a thousand years, gaining power in secret while the Jedi still believed that the Sith had been destroyed. During this period, the Dark Lord of the Sith Darth Plagueis took Darth Sidious, the Sith persona of Senator Sheev Palpatine of Naboo, as his apprentice. They worked for years to coax the final secrets from the dark side of the Force. Sidious called back on the wisdom of Plagueis as a planner and a prophet, knowing full well that two Sith were required to enact their means; one to serve as bait for the dark side, the other to be the vessel. Success would allow them the ability to harness the full power of the dark side and rule immortal for ten thousand years.

Sidious and Maul
"Always two there are; no more, no less. A master and an apprentice."

- Yoda

While training under Plagueis, Sidious acquired a Dathomirian Zabrak named Maul as his pupil. Seeing no further use for his master, Sidious killed Plagueis in his sleep.

In 32 BBY, during the Invasion of Naboo by the Trade Federation, the Sith finally revealed themselves to the Jedi with Sidious sending Maul to Tatooine to capture Queen Padmé Amidala and take her back to Naboo so she could sign a peace treaty. The Jedi Qui-Gon Jinn faced Maul but was able to leave Tatooine with Amidala and his allies, realizing that the Sith had returned. During the Battle of Naboo, which broke the Federation's blockade, Maul was seemingly killed by Padawan Obi-Wan Kenobi, leading the Jedi to realize the return of the Sith.

Sidious and Tyranus
"Remember, the first and only reality of the Sith&hellip; there can only be two. And you are no longer my apprentice. You have been replaced."

- Darth Sidious, to Darth Maul

With Maul gone, Sidious took the former Jedi Master Count Dooku as his next apprentice and bestowed him the name Darth Tyranus. In his early days as an apprentice, however, Dooku wasn't totally adherent to the Rule and considered recruiting the Jedi Knight Jak'zin to the Sith cause, but ultimately stopped when Sidious threatened to replace him with the Togorian Jedi. During the next decade, Dooku aided his master in engineering the Clone Wars, including orchestrating Jedi Master Sifo-Dyas' death, and then to use his name to order an army of clones to be created for the Republic and selecting bounty hunter Jango Fett as the genetic template for the clones. In 22 BBY, with the Confederacy of Independent Systems on their side, Dooku revealed his new allegiance to the Jedi and the Clone Wars began with the Battle of Geonosis.

During the war, the Rule of Two was violated by Dooku. During the initial stages of the conflict, Dooku took the Dathomirian Nightsister Asajj Ventress on as an assassin. However, Sidious, believing Dooku may have been training her to destroy him and sensing that her power had grown, ordered Dooku to eliminate her. Dooku obeyed his master and left her for dead following the Battle of Sullust. Dooku later took the Zabrak Savage Opress, brother of Maul, as his apprentice only for his plan to fail due to Ventress' intervention. Maul later revealed himself to be alive and took Opress as his apprentice, making two rival pairs of Sith. However, Sidious tracked them down and killed Opress during the Mandalorian civil war, whilst allowing Maul to live as he had other uses for him. Dooku took the Jedi Master Quinlan Vos as his apprentice after capturing him, but his plan failed again as Ventress gave her life to save Vos.

Sidious and Vader
In 19 BBY, shortly before the end of the Clone Wars, General Grievous kidnapped Palpatine, leading Kenobi and Anakin Skywalker to be dispatched to rescue him aboard the Invisible Hand. During a lightsaber duel aboard the ship, Skywalker killed Dooku before the trio eventually made it back to Coruscant escaping. Student less again, Sidious seduced Skywalker to the dark side by telling him about Plagueis upon discovering his fears that Amidala, his secret wife, would die in childbirth. Skywalker initially revealed Palpatine's secret to Mace Windu, who then attempted to arrest the Chancellor. Skywalker, however, was forced to turn on the Jedi to save Palpatine from being killed. No longer a Jedi, Skywalker became Sidious' final apprentice, who bestowed him the name Darth Vader. Sidious issued the clone troopers to turn against their Jedi Generals and Skywalker was sent to the Jedi Temple to kill the Jedi there. Afterwards, Skywalker traveled to Mustafar where he slaughtered the Separatist Council whilst Palpatine proclaimed himself Emperor and reorganized the Republic into the First Galactic Empire. After the failure of Yoda and Kenobi to finish off Sidious and Vader, Sidious saved Vader from dying on Mustafar, encasing him in armor.

Informal apprentices and potential replacements
During the Imperial Era, Vader taught the Inquisitorius, a group of former Jedi who had turned to the dark side, and were tasked with hunting down the remaining Jedi, though the Inuqisitors themselves only served the Sith and were not considered Sith apprentices. By 0 BBY, the Inquisitorius ceased to exist.

Though seemingly invincible, the New Order was put in danger when the Alliance to Restore the Republic succeeded in destroying the Death Star battle station. Doubting Vader's capacities, Sidious accepted Doctor Cylo's suggestions in relegating Vader to a ceremonial apprentice and replacing him with a new biologically engineered one. When Vader met Cylo's creations, Commander Karbin, Tulon Voidgazer, twins Morit and Aiolin Astarte, a Trandoshan; he became confused. Vader, eventually proved himself to his master and killed each of Cylo's creations and Cylo himself.

Vader's conspiracy
Unknown to Sidious, however, Vader had already plans to dispose of him and taking Luke Skywalker, his secret son and the pilot who destroyed the Death Star to join him and rule the galaxy. While trying to recover the Emperor's respect before Cylo's death, Vader became aware of his parenthood after the bounty hunter Boba Fett discovered the pilot's name and informed Vader of this. Focused on trying to get his son to join him the dark side, Vader killed Karbin and prevented Luke from being captured on Vrogas Vas. In 3 ABY, following the Battle of Hoth, Vader communicated with Palpatine aboard the Executor, as the Emperor had sensed the threat Skywalker posed to the Sith. Promising his master that Luke would choose over joining them or die, Vader managed to capture the crew of the Millennium Falcon on Cloud City and manipulated Luke into saving his friends.

Upon arriving on Cloud City, Bespin, Luke was unable to hear Leia Organa's warnings that Vader had set up a trap for him. Luke found Vader and the two engaged in a duel. Vader was able to defeat and cut off one of his hands before telling him that he was his father. Vader offered Luke the chance to join him and overthrow the Emperor and bring order to the galaxy. Luke refused and plunged himself into the shaft only to be rescued by the Falcon.

End of the Sith
One year later, both the Empire and the Rebel Alliance were preparing for a definitive showdown above the Forest Moon of Endor with the second Death Star's superlaser finally operational. Still determined to find his son, Vader was sent by his master to Endor to wait for Luke to come to him. After Luke turned himself over to Vader, Luke attempted to turn Vader back to the light side of the Force. Vader refused his son's pleas and the two traveled to the Death Star where Sidious awaited.

Once in the Emperor's Throne Room, the Emperor welcomed Skywalker, promising to complete his training. Eventually a duel broke out between Luke and Vader, ending with Luke cutting off his father's hand. The Emperor prompted Luke to kill his father and take his place at the Emperor's side. Luke refused, stating he was a Jedi like his father before him.

Sidious, enraged, began electrocuting Luke with Force lightning. Vader realizing that he had to choose between saving his son or letting him die, chose to grab Sidious and threw him into a reactor shaft, killing his master but sacrificing himself in the process. Vader had redeemed himself and had become Anakin Skywalker once again, declaring that Luke was right that there had still been good in him, before he died. Anakin's actions had brought balance to the Force, by destroying the Sith as he had been prophezied to do, and by ending the Rule of Two.

Legacy
Thirty years after the defeat of the Sith, the dark side warrior Kylo Ren, who was the grandson of Anakin Skywalker, disposed of his master Supreme Leader Snoke to take the reins of the First Order in an act worthy of the Rule of Two.