Darth Gean was a Twi'lek female who was apprenticed to Dark Lord of the Sith Darth Gravid, as part of the Order of the Sith Lords. Around 533 BBY, Gean learned that Gravid, who attempted to blend Jedi doctrines with his Sith teachings, was trying to destroy all the various Sith artifacts, tomes, and holocrons that contained Sith teachings. Gean penetrated the Force shields that Gravid had placed around the bastion that they had built together on the planet Jaguada and was able to kill her Sith Master. Nevertheless, during the fight, Gravid grievously injured Gean, which forced her to wear prosthetics. She eventually took an apprentice of her own, continuing the lineage instituted by Darth Bane.
A Twi'lek female was sensitive to the Force, eventually becoming the Sith apprentice of Dark Lord of the Sith Darth Gravid and taking the name Darth Gean. During her tenure as Gravid's pupil, Gean helped her Sith Master construct a bastion on the planet Jaguada. However, Gean's Master had begun to lose his sanity, because he attempted to combine Jedi philosophies, such as benevolence and empathy, into his Sith teachings.
At some point around 533 BBY, Gravid—who had concluded that his repository of Sith holocrons and tomes needed to be destroyed so that he could rebuild the organization—used the Force to raise barriers around his bastion and began eradicating the Sith knowledge in his possession. Gean broke through the shields around their stronghold and confronted her Master in a duel. During the fight, Gean was gravely injured after Gravid cleaved off one of her arms and shoulders as well as the left side of the Twi'lek's face and chest. However, Gean gained the upper hand, killing Gravid despite being unarmed.
After the confrontation, Gean acquired prosthetics to replace the limbs she had lost. She eventually took an apprentice of her own and continued with the Grand Plan—which was instituted by Darth Bane, the founder of the Order of the Sith Lords—to topple the Jedi Order and the Galactic Republic. In taking her apprentice, Gean continued the Rule of Two, an ordinance also instituted by Bane that restricted the Sith to a single Master and apprentice. Darth Plagueis, recounted her actions to his apprentice, Darth Sidious, believing her to be courageous.
After discovering Darth Gravid's plan to destroy the Sith teachings, Darth Gean displayed complete dedication to the dark side of the Force and the Sith Order by fighting and murdering her Master, despite being seriously injured in their duel.
Darth Gean was sensitive to the Force and was powerful enough to break through her Master's Force barriers around his fortress. She was also able to survive the confrontation with Gravid, despite being grievously injured and being forced to wear prosthetics as a result. According to Darth Plagueis, the Twi'lek's power with the Force was not obstructed on account of her cybernetics.
Darth Gean was introduced in the 2012 novel Darth Plagueis, written by James Luceno. Her character was created to explain some of the background of the Order of the Sith Lords.