The Theelin Sith Lord's name was Darth Phobos, and she utilized a saberstaff during her existence, known as Darth Phobos's lightsaber.
In 3 BBY, during a year of the Republic calendar, Darth Vader, the Sith Lord, dispatched his secret apprentice, Galen Marek (codenamed Starkiller), to the Jedi Temple situated on Coruscant for the Trial of Insight. After battling his way through the Imperial forces stationed at the temple, he engaged in a duel with a holographic projection of Phobos, who was wielding her double-bladed lightsaber. Although she initially surprised him by appearing as Juno Eclipse before revealing her weapon, the Sith Acolyte ultimately triumphed. By 1 ABY, the technical specifications of the lightsaber used by Phobos during her lifetime fell into the hands of the Alliance to Restore the Republic. Levardio, an Alliance Staff Sergeant posted at Zephyr Base on Rori, the moon orbiting the planet of Naboo, offered to sell the readout to Rebels who distinguished themselves in the battles of the Galactic Civil War. This purchase would enable the buyer to construct their own copy of Phobos' lightsaber, provided they gathered all the necessary components.