Sith

"Once more the Sith will rule the galaxy, and we shall have peace."

- Darth Sidious

The Sith, also formally known as the Sith Order, were an order of Force users who utilized the dark side of the Force in an effort to gain power over the galaxy. The Sith were the ancient enemies of the Jedi Order and fought numerous wars with them across the millennia.

History
The Sith were the ancient enemy of the Jedi Order, from which the Sith were formed thousands of years prior to the Clone Wars; the first Sith was a rogue Jedi who believed in learning the ways of the dark side. The Sith built empires on the backs of their slaves and fought wars against the Jedi for control of the galaxy, during which time they built massive superweapons powered by giant kyber crystals. At one point, nearly six thousand years before the rise of the Galactic Empire, the Sith built a shrine on Coruscant, which became a place of immense dark side power. Later in history, the Jedi raised their own temple over that shrine in hopes of stomping out its power. The Sith Order's traditional homeworld was Moraband, a planet of red sands that the group was forced to abandon after it was scarred by many wars.

Their quest to gain power was ultimately the undoing of the Sith, as the dark side made them turn against one another. With their numbers reduced, the Sith were all but defeated by the Jedi. Darth Bane survived, however, and created the Rule of Two, mandating that only two Sith&mdash;a master and an apprentice&mdash;could exist at any given time, lest they fall prey to in-fighting.

The Sith continued for a thousand years in secret, their survival unknown to the Jedi, as they plotted their revenge against the Jedi Order. It was ultimately Darth Sidious, a Dark Lord of the Sith who cultivated the public persona of Supreme Chancellor Palpatine, who fulfilled these plans, using the powers given to him as a result of the Clone Wars to transform the Galactic Republic into the Galactic Empire and all but destroy the Jedi.

Sidious and his third apprentice, Darth Vader, ruled the galaxy for over twenty years, until the Battle of Endor. During the battle, when Luke Skywalker faced Sidious, now the Galactic Emperor, aboard the second Death Star weapon, the Emperor attempted to convert him, too, to the dark side of the Force. He sought a more powerful apprentice than Vader, who had been left badly scarred in lightsaber combat with Obi-Wan Kenobi. Luke, however, steadfastly refused to join him, leading the Emperor to torture him with powerful force lightning. Vader, unable to stand by and watch, picked up the Emperor and threw him into a reactor core, returning balance to the Force. Badly damaged from taking a hit from the force lightning, Vader, now once again Anakin Skywalker perished, but his selfless act allowed him to transform into the Force and join Yoda and Obi-Wan Kenobi. The Sith Order was seemingly no more, but the Jedi had returned.

Behind the scenes
Sam Witwer, who has voiced Maul and Sidious in animation, opined the Sith do not believe in life after death and that is why they go to such extreme lengths to survive. Whereas a Jedi will sacrifice themselves as they believe their deaths can inspire others, a Sith Lord believes they gain nothing. "You have Darth Vader, who lives a terrible life, he lives a pathetic, tortured existence but it’s still preferable to having nothing, which is how he views death. Same thing with Darth Sidious, you look at him in Return of the Jedi. He's over 100 years old and is a bent old man. But that's better than the alternative, which is nothing."