Irizi'stal'mustro, known as Zistalmu, was a Chiss male who served first as an Aristocra and later as a Syndic of the Irizi family within the Chiss Ascendancy's Syndicure.
Despite the Irizi family rivalry with the Mitth family, Zistalmu covertly partnered with Syndic Mitth'urf'ianico to try to sabotage the career of Senior Captain Thrawn.
Later he even became Syndic Prime and joined Patriarch Irizi'fife'rencpok to the Circle of Unity meeting with the other Patriarchs of the Nine Ruling Families.
At some point after the Lioaoin pirate campaign and before the Vagaari pirate operations, Councilor Zistalmu was tasked with recruiting Senior Commander Mitth'raw'nuru, then a merit adoptive of the Mitth family, to join the Irizi family. Zistalmu understood why the Irizi wished to recruit the Commander, but wondered if they had gone mad. Zistalmu knew that Thrawn was a brilliant military strategist, but was also aware of the officer's potential for political embarrassment. Zistalmu offered Thrawn to join the Irizi as a Trial-born, meaning Thrawn would not have to perform the Trials. Thrawn later asked his friend Ar'alani for her advice on whether he should accept the offer. In the end he decided to stay with the Mitth instead.
Some time after Thrawn's quiet declining of the Irizi offer, Zistalmu would meet with Councilor Mitth'urf'ianico (Thurfian) at the March of Silence in Convocate Hall. They agreed that Thrawn posed a serious threat to the survival of the Chiss Ascendancy and would agree to cooperate to work against him. However, they would fail to stop his rise in the Chiss military hierarchy.
After Thrawn captured a Nikardun vessel in the Rapacc system, now Syndic Zistalmu would join now Syndic Thurfian in rebuking Thrawn's actions. In a meeting with Thrawn, Admiral Ar'alani, and Supreme General Ba'kif, the group would call Thrawn's military encounter in the Rapacc system unauthorized. Zistalmu specifically expresses disbelief that a military tribunal had not yet been scheduled concerning the issue. They also believe that the Nikardun conquests of surrounding nations pose no threat to the Ascendancy.
After Ar'alani had allowed Thrawn to partner with the Garwians for reconnaissance concerning the Nikardun on the Vak Combine homeworld of Primea. Zistalmu and Thurfian held a meeting with Ba'kif and the admiral to express their displeasure. They once again reiterate their belief that the Nikardun are of no interest to the Chiss Ascendancy, as they have no obvious aspirations of a Chiss conquest. Later in the conversation, Zistalmu offers his opinion that Thrawn should be left to fend for himself on Primea. Ba'kif and Ar'alani are insistent on retrieving him with the Vigilant, though, and they have their way. As they discuss their retrieval plan, the subject of Che'ri's caregiver is brought up. Ar'alani had been selected by Che'ri's current caregiver, Mitth'ali'astov (Thalias), who is with Thrawn on his mission, to be Che'ri's substitute caregiver, but Thurfian believes that her duties as admiral takes away from her ability to adequately care for the young sky-walker. As there are no other caregivers available, Zistalmu offers that his wife (who had been a caregiver before they were married) could take up the role until Thalias returns. Despite Ar'alani's protests, Ba'kif agrees to let Zistalmu's wife act as Che'ri's caregiver when the admiral is busy with her other duties.
Before arriving at Primea, Zistalmu reveals to Ar'alani that he doesn't hate Thrawn but, rather, simply opposes the danger he poses to the Ascendancy. Ar'alani asks for clarification, but Zistalmu tells her that she knows what he is talking about, and, if she doesn't, she is choosing not to. Ar'alani does not like this answer, but the Vigilant arrives at Primea before she can demand more clarification. Zistalmu witnesses a Vak patrol craft shoot at the Vigilant using modulated laser fire. Zistalmu correctly determines that this is Thrawn. However, since Thrawn's commandeered patrol craft is now being pursued by other Vak patrol ships, Ar'alani, using the excuse that they do not know for sure that it is Thrawn, decides that it is necessary to start attacking the other Vak ships to ensure Thrawn's safety. Zistalmu heavily questions her actions, but before she can fire upon the Vaks, four Lioaoin ships, summoned by General Yiv the Benevolent, the leader of the Nikardun, arrive behind the Vigilant and fire upon them almost immediately. Ar'alani, recognizing her lack of adequate firepower, recognizes the need for a retreat. Zistalmu admonishers her for wanting to leave when the Vigilant is actually attacked by an enemy. Thrawn, now not being pursued by the Vaks (who do not want to involve themselves in the battle), is able to disable the weapons of the outermost Lioaoin ship, which gives Ar'alani enough time to secure Thrawn's patrol craft and leave the system.
After the Nikardun defeat at the hands of Thrawn, Zistalmu would again meet with Thurfian to discuss his recent military successes. Zistalmu shared that he had to recently speak to Xodlak family representatives, who brought a petition, written by Xodlak Councilor Xodlak'uvi'vil (Lakuviv), asking the Irizi to sponsor the Xodlak attempts to return to Ruling Family status. Zistalmu and Thurfian would agree to establish credible rumors that the Vagaari have aligned themselves with the Paataatus Hiveborn. They hope that Thrawn would be sent far away from the Ascendancy to investigate these rumors and would die or make a monumental mistake in the process. This does not work, however, as Thrawn was able to defeat a secret remnant of the Nikardun at the Paataatus Hiveborn hive-home of Nettehi. In another meeting with Thurfian, Zistalmu proposed that, instead of Thrawn receiving any glory from defeating any potential Vagaari pirate remnants, the Grayshike would be sent to join the Springhawk. Zistalmu explained that the Grayshrike is commanded by a member of the Xodlak family, Senior Captain Xodlak'in'daro (Lakinda), who is allied to the Irizi. He argued that the Xodlak would diminish Thrawn's share of the glory, and Thurfian accepted this idea.
After the Hoxim incident, Zistalmu would learn of Senior Captain Xodlak'in'daro's (Lakinda's) troubles with her Xodlak family. Zistalmu would be sent to recruit her to the Irizi as a trial-born. After a meeting with Lakinda, she would accept the Irizi's offer and would soon be renamed as Irizi'in'daro (Ziinda).