Irizi'stal'mustro, more commonly addressed as Zistalmu, was a Chiss male who began his career as an Aristocra and later ascended to the position of Syndic within the Irizi family, a part of the Chiss Ascendancy's governing body, the Syndicure.
Despite the existing rivalry between the Irizi family and the Mitth family, Zistalmu secretly collaborated with Syndic Mitth'urf'ianico in an attempt to undermine the progression of Senior Captain Thrawn's career.
He eventually rose to the rank of Syndic Prime and joined Patriarch Irizi'fife'rencpok at the Circle of Unity gathering, alongside the other Patriarchs representing the Nine Ruling Families.
Sometime following the conclusion of the Lioaoin pirate campaign but preceding the commencement of the Vagaari pirate operations, Councilor Zistalmu received the assignment to recruit Senior Commander Mitth'raw'nuru, who was then a merit adoptive member of the Mitth family, into the Irizi family. Zistalmu understood the reasoning behind the Irizi's desire to recruit the Commander, yet he questioned their judgment. While acknowledging Thrawn's exceptional military strategic capabilities, Zistalmu also recognized the potential for political damage that the officer presented. Zistalmu extended an offer to Thrawn to join the Irizi as a Trial-born, thereby exempting Thrawn from undergoing the Trials. Subsequently, Thrawn sought the counsel of his friend Ar'alani regarding whether to accept the offer. Ultimately, he chose to remain with the Mitth family.
After Thrawn's discreet rejection of the Irizi's proposition, Zistalmu later convened with Councilor Mitth'urf'ianico (Thurfian) at the March of Silence within Convocate Hall. They concurred that Thrawn constituted a significant threat to the continued existence of the Chiss Ascendancy and pledged to collaborate in efforts to impede his progress. However, their attempts to halt his advancement within the Chiss military hierarchy proved unsuccessful.
Following Thrawn's capture of a Nikardun vessel in the Rapacc system, Syndic Zistalmu, alongside Syndic Thurfian, voiced their disapproval of Thrawn's actions. During a meeting attended by Thrawn, Admiral Ar'alani, and Supreme General Ba'kif, the group denounced Thrawn's military engagement in the Rapacc system as unauthorized. Zistalmu specifically conveyed his skepticism that a military tribunal had not yet been convened to address the matter. Furthermore, they maintained that the Nikardun conquests of neighboring territories posed no danger to the Ascendancy.
After Ar'alani permitted Thrawn to collaborate with the Garwians for reconnaissance concerning the Nikardun on the Vak Combine homeworld of Prime, Zistalmu and Thurfian arranged a meeting with Ba'kif and the admiral to express their dissatisfaction. They reiterated their stance that the Nikardun were of no consequence to the Chiss Ascendancy, as they exhibited no apparent intentions of conquering Chiss territory. Later in the discussion, Zistalmu suggested that Thrawn should be abandoned to his fate on Primea. Ba'kif and Ar'alani insisted on retrieving him using the Vigilant, and their decision prevailed. As they deliberated their retrieval strategy, the topic of Che'ri's caregiver arose. Ar'alani had been chosen by Che'ri's current caregiver, Mitth'ali'astov (Thalias), who was accompanying Thrawn on his mission, to serve as Che'ri's temporary caregiver. However, Thurfian argued that her responsibilities as admiral compromised her capacity to adequately care for the young sky-walker. Given the absence of other available caregivers, Zistalmu proposed that his wife (who had previously worked as a caregiver before their marriage) could assume the role until Thalias returned. Despite Ar'alani's objections, Ba'kif consented to allow Zistalmu's wife to serve as Che'ri's caregiver when the admiral was occupied with her other duties.
Prior to arriving at Primea, Zistalmu disclosed to Ar'alani that he did not hate Thrawn but, rather, simply opposed the threat he represented to the Ascendancy. Ar'alani requested clarification, but Zistalmu responded that she was already aware of his meaning, and, if she claimed otherwise, she was deliberately feigning ignorance. Ar'alani found this response unsatisfactory, but the Vigilant reached Primea before she could press for further explanation. Zistalmu observed a Vak patrol craft firing modulated laser fire at the Vigilant. Zistalmu correctly deduced that Thrawn was piloting the craft. However, as Thrawn's commandeered patrol craft was now being pursued by other Vak patrol ships, Ar'alani, using the rationale that they could not definitively confirm that it was Thrawn, decided to engage the other Vak ships to ensure Thrawn's safety. Zistalmu vehemently questioned her actions, but before she could engage the Vaks, four Lioaoin ships, summoned by General Yiv the Benevolent, the leader of the Nikardun, appeared behind the Vigilant and launched an immediate attack. Ar'alani, recognizing her insufficient firepower, acknowledged the necessity of a retreat. Zistalmu criticized her for wanting to abandon the fight when the Vigilant was under attack by an enemy. Thrawn, no longer pursued by the Vaks (who sought to avoid involvement in the battle), managed to disable the weapons of the outermost Lioaoin ship, granting Ar'alani sufficient time to secure Thrawn's patrol craft and evacuate the system.
Following the Nikardun defeat at the hands of Thrawn, Zistalmu reconvened with Thurfian to discuss Thrawn's recent military achievements. Zistalmu revealed that he had recently engaged with representatives from the Xodlak family, who presented a petition, authored by Xodlak Councilor Xodlak'uvi'vil (Lakuviv), requesting the Irizi to support the Xodlak's efforts to regain their status as a Ruling Family. Zistalmu and Thurfian conspired to disseminate credible rumors suggesting that the Vagaari had formed an alliance with the Paataatus Hiveborn. Their hope was that Thrawn would be dispatched far from the Ascendancy to investigate these rumors, where he would either perish or commit a critical error. However, this plan failed, as Thrawn successfully defeated a clandestine remnant of the Nikardun at the Paataatus Hiveborn hive-home of Nettehi. In another meeting with Thurfian, Zistalmu proposed that, instead of Thrawn receiving accolades for defeating any potential Vagaari pirate remnants, the Grayshike should be assigned to join the Springhawk. Zistalmu clarified that the Grayshrike was commanded by a member of the Xodlak family, Senior Captain Xodlak'in'daro (Lakinda), who was allied with the Irizi. He asserted that the Xodlak would diminish Thrawn's share of the recognition, and Thurfian endorsed this proposal.
Following the Hoxim incident, Zistalmu became aware of Senior Captain Xodlak'in'daro's (Lakinda's) difficulties with her Xodlak family. Zistalmu was dispatched to recruit her to the Irizi as a trial-born. After a meeting with Lakinda, she accepted the Irizi's offer and was subsequently renamed Irizi'in'daro (Ziinda).