Karan S'jet is the main protagonist in the Homeworld saga. She is both leader and prophet to her people, a scientific genius, and eventually, the commander-in-chief of the Kushan Mothership Fleet. Her struggles earned her a nearly deity-like status, especially after she took up the mantle of Fleet Command for the second time.
Karan S'jet is the only major named protagonist in the entire series. The two major parts of the Homeworld series are almost completely based around Karan S'jet and her story as a leader for her people. S'jet is mentioned in passing in Homeworld: Cataclysm, the original game's stand-alone expansion pack during a confrontation between the Bentusi and Kuun-lan.
When the Kushan Mothership project neared completion, Karan's research led her to become interested in the problem of the Mothership's central processing unit (CPU). No computer had successfully auto-managed all the various subsystems - the Mothership was simply too large and system-heavy for even the biggest computer that the Kushan had, and building a mainframe big enough would take up a significant portion of valuable space, as well as not only making the mothership easier to disable (i.e., a bigger, and hence easier to hit, target) but also being a near-impossible maintenance problem - and the Mothership was thus inoperable. However, Karan envisioned an idea that differed radically from those proposed by the engineers and technicians working on the Mothership. She proposed that the Mothership be managed by an organic computer: the brain.
Karan was able to provide enough research to suggest that the Kushan brain, with several nerve trunks laid open and connected through cybernetic implants and wiring to the Mothership's various computers, could effectively manage the Mothership's subsystems. She adamantly insisted on being the subject herself, due to the plan's dangerous and possibly permanent nature. Though met with considerable objection, the idea was eventually approved. Despite her family's objections, Karan S'jet was wired directly into the hyperspace core, and from there to the entire Mothership computer network. She became known as Fleet Command for the duration of the journey to Hiigara.
Karan Sjet's first major test of ability came when the Mothership was launched and subsystems were tested, including the ability to construct vessels, refine minerals, and command the fleet from afar. The Mothership's final test was that of the hyperdrive, whose capability had to be tested before engaging in the journey. A simple miscalculation could end in disaster, sending the Mothership thousands of light years away from its destination. As Fleet Command, it was Karan's job to ensure that such an error did not occur.
The jump's destination was to the Khar-Selim, a support vessel traveling at sublight speeds across the outskirts of the Kharak System. However, when the Mothership arrived, the Khar-Selim had been destroyed. Soon afterward, the Mothership was attacked by the Turanic Raiders, a clan of space pirates and mercenaries. The Kushan emerged from the ensuing battle victorious, and promptly returned to Kharak.
The Fleet returned to find Kharak in flames. It had been destroyed by the Taiidan Empire, a vast dominion under the rule of an ancient enemy of the Kushan. The Mothership's mission had now significantly changed; the very survival of the Kushan was now at immediate stake. The Mothership Fleet quickly rescued the cryo trays, which carried the last remnants of the Kushan people, and began to limp its way to Hiigara.
It took time, but Karan led her people — who now regarded her as a sort of messiah figure — across the galaxy to Hiigara. Though Fleet Intelligence handled most of the decisions, it was Karan who managed the fleet, and would often show compassion where Fleet Intelligence didn't. Karan's kindness led them to several allies, including the Bentusi and a group of Taiidan defectors. As such, Karan more than earned her love amongst the Kushan people.
When Karan reached Hiigara, she insisted to be the last to set foot on the surface, successfully removed from the Mothership and greeted by awaiting gleeful crowds.
Not much is known of Karan S'jet's life between Homeworld and Homeworld 2. She had no role to speak of in Homeworld: Cataclysm, but it is known that she did live on to the time of Homeworld 2, set 100 years after Cataclysm. By the time of Homeworld 2, it seems she had settled down, but still had some influence amongst the Kushan people. She was a living legend, of course, and although those governing the planet were no longer her colleagues and comrades from the journey to Hiigara, she was still a popular figure.
When the second Mothership Fleet was surprised shortly after completion by a Vaygr attack, she managed to escape with the Pride of Hiigara intact. Over time, her role would bring her formal religious significance: according to legend, they that possessed the three hyperspace cores would be known as the Sajuuk-khar — the chosen of God — and their leader as the Sajuuk'Khem, the Manipulator of He Whose Hand Shapes What Is.
Karan would eventually recover the other two hyperspace cores, one from the wreckage of Bentus and one from the wreckage of Makaan's flagship. With all three she reactivated the ancient vessel Sajuuk, and became the Sajuuk'Khem, leaving the Pride of Hiigara behind. Using this newfound asset, the Hiigaran fleet was able to reclaim the Homeworld from the Vaygr siege, bringing about a time of peace under Karan's guidance.