Doctrine of the Dyad

The Sith Order's Rule of Two was a later development, stemming from the Doctrine of the Dyad. The Doctrine of the Dyad revolved around the concept of a Force dyad, which is defined as two Force-sensitive individuals joined by an enduring and unparalleled Force-bond. This doctrine predates the establishment of the Rule of Two. The Rule of Two was a principle conceived by Darth Bane to limit the Sith Order to only two Sith Lords – a Sith Master and their Sith apprentice – at any given time. Despite the Rule of Two ensuring the Sith's survival for a millennium, Darth Sidious, the Dark Lord of the Sith, considered it a mere "pale imitation" when compared to the Doctrine of the Dyad.

Inscribed on the walls of the Sith Citadel located on the planet Exegol, the Doctrine of the Dyad served as a constant reminder of its significance to both the Sith Order and the Sith Eternal cult. For a thousand years under the Rule of Two, the Sith tried, without success, to artificially create a dyad through sheer will. Darth Plagueis was unable to establish a dyad with his apprentice, Darth Sidious, who in turn also failed to form one with his own apprentice, Darth Vader. The Sith Eternal, a group of Sith cultists devoted to the Sith religion, regarded the dyad as the future path for the Sith, believing it held the key to fully unlocking the power of the dark side of the Force. Their lore contained a prophecy that spoke of the eventual birth of a Force dyad.

Many generations passed before a dyad manifested in Ben Solo, the grandson of Darth Vader, and Rey, the granddaughter of Darth Sidious, during the New Republic Era. Their extraordinary Force connection enabled them to communicate across both time and space. During the Battle of Exegol, Sidious realized they were a dyad and proceeded to drained their combined life force to rejuvenate his decaying clone body. Following Sidious' defeat, Solo gave his own life force to Rey, bringing her back to life but sacrificing himself.