Rule of Two

The Rule of Two doctrine, also called the Banite system and known as Chwayatyun in Sith, was the guiding principle of the Order of the Sith Lords after the internecine New Sith Wars. It replaced the practices of Lord Kaan's Brotherhood of Darkness, which claimed equality among Sith Lords and forbade the use of the title "Darth."

The Rule of Two was instituted by Darth Bane, once a student at Kaan's Sith academy, in response to what he viewed as inevitable, self-destructive infighting within the Sith Order. The Rule of Two states that there would be only two Sith at one time, a master and an apprentice, guaranteeing that when the apprentice becomes powerful enough in the ways of the dark side to take the title of master, only then would they be worthy of the title. This transfer of power would only take place when the apprentice takes their master's life and finds a worthy student to repeat the cycle, this way the Sith will grow more powerful and still exist through the new master. Both master and apprentice were considered to be Sith Lords.

The practice survived with varying levels of enforcement for a thousand years until the murder of Darth Tenebrous at the hands of his apprentice in 67 BBY— Darth Plagueis held the doctrine in contempt, and intended to live forever together with his own apprentice, Darth Sidious. Although the latter betrayed and murdered his master in accordance with the Rule of Two and trained apprentices of his own, never more than one at the same time, he did not fully accept it, following instead his own Rule of One, in order for him to continue as the ruler of the Sith.

Text and facts from the “Rule of Two/Legends” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.