Eldon Ax, originally named Cinzia Xandret, was a Human female Sith who lived during the eras of the Great Galactic War and the Cold War. She was the daughter of technician Lema Xandret, but was taken from her family and trained in the Sith Academy under the tutelage of Darth Chratis. At 17 years old, the truth of her past was revealed to her, along with evidence suggesting her family was now considered traitors to the Sith Empire. Ax then spearheaded the search for the family's planet, ultimately leading both the Sith Empire and the Galactic Republic to Sebaddon. The two factions then formed an unusual alliance to eliminate the hex droids created by Lema Xandret, which posed a threat to the entire galaxy. As a high ranking member of the Empire, Ax encountered a clone of her own, and seized control of the droids, preventing them from killing their master and ultimately deactivating them.
As a child, Cinzia Xandret was abducted from her mother, Lema Xandret, a droid maker, by Darth Chratis. Because Lema Xandret refused to surrender her daughter to the Sith, she was condemned to execution. However, Lema Xandret evaded her death sentence by escaping with other droid makers. To prevent Cinzia from remembering her past, Darth Chratis used the Force to create a mental block in her mind, and gave her the new name Eldon Ax.
After being defeated in combat by a Mandalorian named Dao Stryver, Ax was questioned by her, who was seeking information about Lema Xandret and a ship called Cinzia. Later, the wreckage of the Cinzia was discovered and put up for auction by a Hutt named Tassaa Bareesh. Before revealing this information to the Sith Dark Council, Darth Chratis removed the mental block he had placed on Eldon Ax and revealed the truth about her origins. The Dark Council dispatched Chratis and Ax to retrieve the remains of the Cinzia and, if found, execute Lema Xandret. During the attempt to steal the Cinzia wreckage, deadly and mysterious hex droids appeared and foiled the theft. Although the mission failed, Ax managed to trace the origin of the hex droids back to the planet Sebaddon using a hex remnant. The Jedi were also able to do the same. Ax then accompanied her master to claim the planet for the Empire.
Upon their arrival at Sebaddon, the hexes launched a fierce defense, inflicting heavy damage on both the Republic and Imperial fleets. A temporary truce and alliance were forged between the two fleets to combat the hex threat. To solidify the agreement, Chratis insisted that Ax accompany Jedi Grand Master Satele Shan, while he would take Shan's Padawan Shigar Konshi. During the battle, Ax discovered a clone of herself being preserved in a tank of amniotic fluid. Ax also discovered that her mother had been killed by her own Hex Droid creations, but continued to exist and speak to her clone through the amnioid fluid. Ax learned from her clone that the Hex Droids were created to protect her. Upon being released from the tank, the clone died instantly, but not before instructing Ax to input her DNA into the hex computer. The hexes recognized Ax as Cinzia and obeyed her commands. Eldon Ax ultimately killed her master, Darth Chratis, by ordering the hex droids to attack him during the battle on Sebaddon. She then commanded them to self-destruct. Later, she became the apprentice of Darth Howl, a member of the Dark Council.
Ax was a shrewd young woman, capable of assassinating her own master and concealing the act. Recognized by the Dark Council, she eventually earned the position of full apprentice to Darth Howl, a significant accomplishment within the ruthless ranks of the Sith Empire.
After discovering her origins, Ax, despite her loyalty to the Sith, desired her mother's death for her betrayal and openly expressed this sentiment, even to the Jedi.
Ax possessed a limited ability to generate Force lightning and was a skilled lightsaber duelist. Despite her youth, she was also proficient in using Force barrier to shield herself from severe injuries when focusing her rage, although she could still be overwhelmed when outnumbered or distracted, as demonstrated in her encounters with the Mandalorian Dao Stryver.