The Order of the Sith Lords, also known as Bane's Sith Order, Banite Sith, or simply the Sith, was an ancient organization of Force-sensitives who utilized the dark side of the Force. Founded approximately one thousand years before the Battle of Yavin by the Sith Lord Darth Bane, it was intended to replace the Brotherhood of Darkness and institute a rebirth of the Sith. The guiding principle of the Order was the Rule of Two, which was developed by Bane through the teachings of Darth Revan's Holocron. Under this new tenet, only two Sith Lords were allowed to exist at any given time; a master and an apprentice. The Rule stipulated that after learning everything the master had to teach, the apprentice would attempt to kill the master and take an apprentice of their own. The intended effect of this rule was to ensure that each successive master would be stronger than the last. Ultimately, Bane intended that his successors would be able to amass enough power in secret to engineer the fall of the Republic and the destruction of the Jedi Order.
Bane's expectations of the new Order were met with his death at the hands of his own apprentice, Darth Zannah. The tradition was carried on over the next millennium, even though many Sith who followed in Bane's lineage were appalled at the thought of being slain by their own apprentices. After centuries of operating in secrecy, the Grand Plan for revenge was initiated by the Sith Lords Darth Plagueis and Darth Sidious. Sidious, who usurped his Master's position, ultimately fulfilled Darth Bane's dream: the return of Sith dominance throughout the galaxy. With the betrayal and near destruction of the Jedi Order, Sidious dissolved the Galactic Republic and replaced it with the Galactic Empire. Ruling as emperor in his public guise as "Palpatine", Sidious' reign was prophetically ended by his own apprentice—the Chosen One, Anakin Skywalker. Though he returned in the form of several clones, each inhabited in turn by the Emperor's dark spirit, Sidious' final demise in 11 ABY ended the line of Bane and Zannah.
The collapse of Darth Bane's Sith Order, however, did not bring about the final end of the Sith itself. Lumiya, a former Hand of Emperor Palpatine and the self-proclaimed Dark Lady of the Sith, formed her own Sith and incorporated the Rule of Two in its philosophy. She regarded her greatest achievement in the form of her apprentice Darth Caedus, a grandson of Anakin Skywalker and the first active Sith Lord since the reign of Darth Sidious. During the time of Lumiya and Caedus, another Sith Order had come into existence, one that was far less connected with the old Order of Darth Bane. The One Sith, founded by the former Jedi A'Sharad Hett, rejected the Rule of Two. Under the Rule of One, the new organization permitted the existence of many Sith Lords, all of whom ultimately answered to the authority of a single Dark Lord.