Thistrian, a male Chiss belonging to the Mitth family within the Chiss Ascendancy, held a prominent position in their society. By the year 19 BBY, he was the Speaker representing the family in the Chiss Syndicure, which served as the governing body of the Ascendancy. Following Mitth'raw'nuru, known by his core name as "Thrawn," being made a Mitth Trial-born, the Speaker communicated with Aristocra Mitth'urf'ianico, "Thurfian." He explained he was compelled to do so because the Irizi family had also offered Thrawn the same status within their family. Around 18 BBY, Thistrian was one of the Mitth's Patriels, managing the family's affairs on the planet Avidich within the Ascendancy. When the Grysk agent "Jixtus" proposed providing Thistrian with Grysk warships to safeguard his family, the Patriel informed Thurfian, who had risen to the position of Mitth Patriarch, of the Grysk's proposition. Under the Patriarch's orders, Thistrian dismissed Jixtus.
In 19 BBY, Thistrian, a senior male Chiss belonging to the Mitth ruling family of the Chiss Ascendancy, was the Speaker for his family within the Chiss Syndicure, the Ascendancy's governing council. In this capacity, he presided over the Mitth members of the Syndicure. After the Irizi ruling family extended an offer to Mitth'raw'nuru, "Thrawn," a merit adoptive with the core name serving in the Ascendancy's Expansionary Defense Fleet, the Speaker was compelled to grant Thrawn the Mitth rank of Trial-born, which surprised Aristocra Mitth'urf'ianico "Thurfian." The Aristocra considered Thrawn a threat to his family and conveyed this sentiment to the Speaker during a comm conversation.
Believing Thrawn could bring honor to the Mitth through his military service or achieve something that would "raise the Ascendancy to heights it had never achieved," Thistrian felt the Mitth should retain Thrawn over the Irizi. He informed Thurfian that the Expansionary Defense Fleet's Defense Hierarchy Council had assigned the merit adoptive command of the Chiss heavy cruiser Springhawk, and he investigated Picket Force Two's assignment upon learning of discussions to appoint Thrawn as the task force's commander. Given that Picket Force Two was tasked with patrolling beyond the Ascendancy's east-zenith border, the Speaker believed Thrawn would not cause issues, as the only entities in that region were the Paataatus Hiveborn and various pirate factions.
Around 18 BBY, Thistrian assumed the role of one of the Mitth's Patriels, overseeing the family's affairs on Avidich, an Ascendancy world. Following the visit of the Kilji Illumine war cruiser Whetstone to the Ascendancy, it proceeded to Avidich. The Grysk operative known as "Jixtus," accompanying the Whetstone's commander, Generalirius Nakirre, engaged with the Patriel, providing him with a recording of a battle involving the Dasklo, Erighal, Pommrio, and Xodlak famlies. The Grysk asserted that the families were planning an alliance and offered to sell further information—confirmation of the participants, the battle's location, and the conflict's purpose—to Thistrian.
After the Patriel positioned a Mitth frigate and missile boats for combat, Thistrian contacted Thurfian, who had become the Mitth Patriarch. He presented Thurfian with the recording provided by Jixtus and, at the Patriarch's request, an enhanced version from the Patriel's technicians. Thistrian also reported the operative's offer of several Grysk warships capable of reaching the Ascendancy within a few [days](/article/standard_day]. Thurfian deemed the Grysk's offering a "meager of information," prompting Thistrian to emphasize that if the battle foreshadowed a Dasklo–Pommrio–Xodlak alliance, the Mitth could face a significant threat. However, the Patriarch, angered by Jixtus's offer of military vessels to the Mitth, dismissed the Patriel, instructing him to send Jixtus away. Thistrian complied with Thurfian's command, and Jixtus departed Avidich.
As an older Chiss, Thistrian possessed a tendency to be talkative when the mood struck him. Despite learning much from the Patriel, Thurfian hoped that the day he spoke with Thistrian after the older Chiss's encounter with Jixtus would not be one where the Patriel was garrulous. Firmly believing that Thrawn could elevate the Ascendancy to unprecedented heights, Thistrian was convinced they should not allow the Irizi to claim the glory that the merit adoptive's successes could bring. He jokingly remarked that whatever Thrawn did would be entertaining to witness.
Thistrian made his initial appearance in the flashbacks of the 2020 novel Thrawn Ascendancy: Chaos Rising, the inaugural volume of Timothy Zahn's Star Wars: The Ascendancy Trilogy.