Doctrine of the Dyad

The Doctrine of the Dyad was a concept centered on the Force dyad, a pairing of two Force-sensitive beings linked by a unique Force-bond that was unbreakable. It was the predecessor of the Rule of Two, a decree developed by Darth Bane to limit the Sith Order's ranks to two Sith Lords—a Sith Master and a Sith apprentice—at any given time. Although the Rule of Two ensured the survival of the Sith for a millennium, the Dark Lord of the Sith Darth Sidious called it a "pale imitation" of the Doctrine of the Dyad.

The Doctrine of the Dyad was etched into the walls of the Sith Citadel on the planet Exegol, where it served as a reminder of its importance to the Sith Order and the Sith Eternal cult. For a millennium under the Rule of Two, the Sith unsuccessfully tried to create a dyad through force of will. Darth Plagueis failed to form a dyad with Darth Sidious, his apprentice, who in turn failed to create a dyad with his own apprentice, Darth Vader. The Sith Eternal, a group of Sith cultists that followed the Sith religion, believed that the dyad was the future of the Sith—the key to unlocking the full potential of the dark side of the Force. A prophecy in the Sith Eternal's lore foretold the birth of a Force dyad.

Entire generations passed before a dyad was born in Ben Solo, the grandson of Darth Vader, and Rey, the granddaughter of Darth Sidious, during the New Republic Era. Linked together through a rare and powerful Force connection, their bond as a dyad allowed Solo and Rey to communicate across time and space. During the Battle of Exegol, Sidious discovered their nature as a dyad and drained the combined life force of Rey and Solo to heal his weakened clone body. After Sidious' destruction, Solo transferred his life force to Rey, resurrecting her at the cost of his life.

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