The Rule of Two was a doctrine created by Darth Bane upon the creation of the Order of the Sith Lords. The rule forbid more than two Sith at one time. Bane stated that under this rule, there could only be one master to embody power and one apprentice to crave it. This rule was practiced at least until the time of Darth Plagueis.
- Star Wars: Episode I - The Chosen One (First appearance)