Darth Bane, born under the name of Dessel, was the Sith'ari and the Dark Lord of the Sith responsible for creating the Rule of Two. Born in 1,026 BBY, he was raised as a poor miner on the Outer Rim planet Apatros.
After killing a Galactic Republic ensign in a fight in 1,003 BBY, Dessel was in danger of being arrested and imprisoned by the Republic. With the help of his friend Groshik, he escaped off-world to join the Sith Brotherhood of Darkness. Initially serving as a foot soldier in the Gloom Walkers unit, he was recognized as a Force-sensitive and taken to the Sith Academy on Korriban.
The Sith Academy on Korriban
Bane, as he had been christened, quickly became one of the best students at the Academy before he lost his faith in the dark side of the Force. Though Bane was able to regain his confidence in the dark side, he lost his trust in the Brotherhood of Darkness, believing it to be a flawed organization whose leader, Skere Kaan, was a coward and a fool.
Deserting the order, Bane studied the holocron of Darth Revan, and, armed with new knowledge, helped destroy the Brotherhood, allowing him to create his own Sith Order. He then instituted a Rule of Two, which stated that there could be only two Sith at any time in order to avoid the infighting that had plagued the Sith for millennia. He also took both the title of Darth and an apprentice named Darth Zannah.
Birth of a new Sith Order
In 990 BBY, ten years after the destruction of the Brotherhood, Bane sought to learn how to create a holocron, through which he would pass down his knowledge to future Sith Lords. The Sith journeyed to the Deep Core world of Tython to locate the Sith holocron of the ancient Dark Lord Belia Darzu. However, while Bane was on Tython, the Jedi Order learned of his existence and sent a group of Jedi to kill both him and his apprentice.
Once the Jedi arrived, they confronted the two Sith in Darzu's fortress. Though outnumbered, the Sith were able to defeat the Jedi - but at cost - as Bane was grievously injured by his own Force lightning. Zannah then took the injured Sith Lord to Ambria under the healer's hut where she convinced the healer Caleb to help them. Caleb notified the Jedi Council, only to have Zannah use her powers to drive Caleb's assistant Darovit insane. Zannah then killed Caleb and hid herself and Bane. When the Jedi arrived, they killed Darovit, believing him to be the Sith Lord. Thus, the Jedi believed the Sith were at last destroyed and left Ambria.
Seeking a new apprentice
A decade later, Bane began to worry that his apprentice was too weak to overthrow him and assume the mantle of Dark Lord of the Sith, as was necessary under the Rule of Two. He began to research the secrets to prolonging his life by transferring his essence to another body and traveled to Prakith, where he claimed the holocron of the ancient Darth Andeddu.
After returning from Prakith, Bane was ambushed by a team of assassins hired by Caleb's daughter, Serra, and was captured. Taken to Doan, Bane was imprisoned and interrogated, only to covertly gain his freedom soon afterward.
Encountering Zannah on Doan, Bane dueled his apprentice, who sought to become the new Dark Lord. The fight ended in a draw, with Bane escaping and heading to Ambria with Darth Cognus, an Iktotchi assassin skilled in use of the dark side who Bane planned to take as his apprentice if Zannah proved herself weak and unworthy. There, Bane and Zannah engaged in a fateful duel that resulted in the death of the Sith'ari and Zannah claiming the title of Dark Lord.