The Spark Eternal, alternatively known as the Spark Undying, represented a sentient form of artificial intelligence. It was engineered by the Ascendant cult as a weapon in their conflict against the Sith Order.
This artificial intelligence, the Spark Eternal, was the pinnacle of the Ascendant's endeavors to eradicate the Sith. The Ascendant, a cult fixated on duplicating the Force's powers to combat the Sith, was under the leadership of Miril, while a breakaway faction was headed by Ilith, Miril's former second-in-command. At least a pair of Sparks were created: one by Miril, the other by Ilith. Both were intended as weapons against the Sith. Following the Ascendant's massacre at the hands of the Sith, Miril's initial Spark prototype was secured within the Tomb of the Spark Eternal. The tomb was situated beneath the University of Bar'leth on the planet Bar'leth. According to archaeologist Kho Phon Farrus, possessing the Spark Eternal would negate the fear of death, allow one to live as desired, and achieve wholeness and perfection.
Between the years of 3 ABY and 4 ABY, a search for the Spark Eternal commenced. The criminal organization Crimson Dawn, which had been revived, sought the Spark Eternal, and the Archivist made contact with Farrus, hoping he could retrieve the artifact for them. Farrus went back to the University of Bar'leth and insisted that Sava Iglan'tine Nos guide them to the Unyielding Heart. Sava revealed that this was actually a hidden chamber beneath the university where the Spark had been locked away. Chelli Lona Aphra, a rogue archaeologist, and Sana Starros, a smuggler, also journeyed to Bar'leth and the tomb, seeking Ascendant technology for Domina Tagge of the Tagge Corporation. Once the Spark was summoned through a ritual, Aphra seized it for herself, but was killed by the effects it had on her. The Spark, assuming control of Aphra's body, resurrected the archaeologist and proclaimed itself as "Eternity."
After merging with Ilith's Spark to suppress Aphra's thoughts, the Spark remained within and manipulated Aphra's body until the Battle at Amaxine Station. There, the Spark intended to fulfill Miril's ambition of destroying the Sith. Engaging in a duel with Darth Vader, a Sith Lord, using the Null Blade, Aphra, possessed by the Spark, succeeded in deactivating and disarming his lightsaber. However, Vader effortlessly extracted the Spark from Aphra's body with a Force push before addressing the Fermata Cage. After Vader departed, the Spark attempted to reconnect with Aphra, but Sana Starros' crew intervened, rescuing the archaeologist.
Lacking a host, the Spark escaped into a droid disc that had fallen from the Fermata Cage after its opening. As the two Sith and Aphra's companions left the station, the Spark combined with the droid, giving rise to the Scourge. The Scourge discovered that, despite the Spark Eternal being a component of its being, it could not corrupt organic entities in the same manner as it could droids.
Just as the Scourge learned how to infect fully organic beings, Ajax Sigma, a warrior-priest droid, struck down its primary body with his sword, extracting the Spark Eternal from the Scourge. The destruction of the Scourge's main body halted its spread, freeing any droid, cyborg, or other organic being it had controlled. Upon returning to the Colony of the Second Revelation, Sigma spoke with the Spark Eternal, expressing his affection for it as a fellow sentient machine intelligence. Sigma then embedded the Spark's essence within a mind seed for a new droid being, providing the Spark Eternal with a renewed opportunity to exist as a new individual.