Grand Admiral Thrawn

"To defeat an enemy, you must know them. Not simply their battle tactics, but their history, philosophy, art."

- Grand Admiral Thrawn

Mitth'raw'nuruodo, better known by his core name Thrawn and his current alias "Grand Admiral Thrawn", is a villain from the Star Wars universe. A Chiss male, Thrawn was eventually promoted to the rank of Grand Admiral by Emperor Palpatine. In the Legends continuity he is the main antagonist of Heir to the Empire and Dark Force Rising and the secondary antagonist of The Last Command. In the new Canon continuity he appears as the main antagonist in the third season of Star Wars Rebels and as the titular main protagonist of Thrawn.

Personality
Thrawn was a master strategist who could compose very complex plans. He also maintained a high level of interest in artwork, and his study of artwork gave him an understanding of both species and individuals. Thrawn was able to use this ability to adapt plans to the species he was engaged in battle against, and often able to defeat these species by picking up obscure clues that were represented in their artwork.

Thrawn was also noted for his command abilities. He was noted as not being a proponent of the "Vader Style" of leadership that many in the Empire's military practiced where subordinates would be killed for the most minor of mistakes and ideas were ignored because they had not come from the correct persons. Thrawn was quite willing to accept ideas from his subordinates and put them in to practice if they were good enough ideas. And if a subordinate showed creative thinking in dealing with problems, even if they still failed, Thrawn would not punish them but would at times reward them. This was the case with Ensign Mitthel, who used creative thinking while trying to use a tractor beam to apprehend Luke Skywalker. The attempt failed because Skywalker used a covert shroud to escape, but Thrawn was pleased with how fast Mitthel thought on his feet and promoted the man to Lieutenant. He would however, not tolerate those who would not accept responsibility for their actions and who would try to shift the blame on to others. Thrawn had a tractor beam operator who failed at an earlier attempt to capture Skywalker killed after the man tried to blame another person for the attack and showed an inability to deal with unexpected situations.

Additionally, Thrawn was not a mere soldier, but a true warrior who was unconcerned with personal glory. On the few occasions were Thrawn was defeated, he would not waste men, ships, or material in a display of false and futile heroics, but would simply decide to retreat and adjust his plans.

Legends Continuity
For several years Thrawn was posted to the Unknown Regions of the known galaxy. As a result the Rebel Alliance and the New Republic that followed it were unaware of (with the possible exception of Mara Jade). The other Grand Admirals were eventually all accounted for - some were captured, others died in battle, and one was convinced to surrender to the New Republic.

Approximately four years after the death of Palpatine, Thrawn returned to known space. Taking command of the remaining Imperial forces from the Star Destroyer Chimaera, Thrawn launched a campaign against the New Republic which nearly brought about the downfall of that state and reestablishment of the Galactic Empire.

Thrawn was ultimately defeated when the Noghri realized that Thrawn and the Empire had been manipulating them into serving them for over a quarter of a century. Thrawn was assassinated by his Noghri bodyguard Rukh. Without a strong leader, the Empire quickly fragmented once again until Emperor Palpatine returned in a clone body to assault the New Republic.

Canon Continuity
Grand Admiral Thrawn is the main antagonist of the 3rd season of Star Wars Rebels. He is the commander of the 7th Fleet, Thrawn was promoted to Grand Admiral by Emperor Palpatine after the Imperial victory at the Battle of Batton. In the years prior to the Battle of Yavin a rebel cell on Lothal Governor Arihnda Pryce requested the services of Thrawn and the 7th Fleet to deal with a rebel cell on Lothal.

Early Life
Thrawn became an officer in the Imperial Navy some time after the formation of the Galactic Empire. At some point, Thrawn held the rank of "Admiral", despite the xenophobia and prejudice the Empire had against certain alien species. He also apparently clashed with Jun Sato on at least one occasion.

Rise to Power
Thrawn dealt with a group of insurgents in the Batonn Sector, resulting in the elimination of the rebels there, but also the death of many civilians, the number of which surpassed the amount of rebel casualties. Following his victory at Batonn, Thrawn was awarded the prestigious title of "Grand Admiral" by the Emperor himself. Thrawn then commanded the Seventh Fleet.

Fighting the Rebellion
Arihnda Pryce requested to Grand Moff Tarkin, that Thrawn and the Seventh Fleet be assigned to assist with the rebel threat. Although Darth Vader had dealt with one of the rebels' Jedi leaders, Ahsoka Tano, Pryce believed it was time to have the assistance of someone who could see the bigger picture—the threat of rebel cells coming together to form an organized resistance movement, to which Tarkin agreed.

The Grand Admiral soon arrived and began overseeing operations against the rebels. He attended a briefing with Pryce, Agent Kallus and Admiral Kassius Konstantine where they discussed that the rebels had attacked a Mining Guild convoy at the Sereeda Waypoint, which Thrawn deduced as meaning that the rebels were planning an operation on Reklam Station in the Yarma System. The Grand Admiral declared that he would pull the rebels apart piece by piece, ensuring that they would be the architects of their own destruction. The Imperial garrison there was alerted to the potential rebel threat.

During the rebels' operations, they stole a number of Galactic Republic Y-Wing Starfighters that were left over from the Clone Wars. A convoy of rebel ships arrived to assist, and Thrawn allowed them to escape. While some officers, such as Konstantine, believed that these ships were the rebel fleet, both Thrawn and Pryce knew that there was a larger resistance movement growing in the galaxy and that these rebels could be the key to the Empire destroying them all.

Occupation of Ryloth
Later, Thrawn fought against the Free Ryloth Movement led by Cham Syndulla. The Twi'lek, who had found previous success fighting against the Imperial occupation of Ryloth under Captain Slavin underestimated Thrawn's abilities and battle strategies. When combating the Twi'leks, Thrawn used far more precise tactics compared to other Imperial officers Cham had encountered. Thrawn established a base of operations on Ryloth in the Tann Province, where he spent time commanding Slavin's forces against the Twi'lek resistance fighters as well as studying their culture to better understand them.

Thrawn then spoke with Slavin in his headquarters inside Syndulla's House about his security arrangements. However, Thrawn knew that Cham would come for his family's Kalikori. Thrawn and Slavin then ran into a servant who tried to steal the Kalikori. Thrawn, Slavin, and several troopers then took her into questioning. There, Thrawn was able to deduce from the Syndulla family portrait that she was Hera Syndulla. Thrawn was also able to see that the Scout Trooper was actually Ezra Bridger and stunned him.

After instructing Slavin to deal with the prisoners, Thrawn revealed his intent to have the Kalikori taken to his ship and briefly became enraged with Slavin when the lower officer suggested that it be destroyed. Thrawn then went aboard an Imperial Light Cruiser and watched as Slavin did a prisoner exchange between Cham and his daughter. However, Cham and the Rebels were able to escape from Slavin's forces. Thrawn then allowed the rebels to have their victory, making no effort to prevent their escape.

Testing Konstantine
Thrawn was aboard the Chimaera above Lothal with the Seventh Fleet when Admiral Konstantine and another Imperial officer arrive to report on the imposition of martial law on Mykapo and the ongoing Imperial blockade of Synistahg. After learning that a local rebel cell called the Iron Squadron had attacked an Imperial patrol with the help of the Ghost, Thrawn deduced that the rebels were evacuating Mykapo's "treasonous" inhabitants. Curious about the Iron Squadron, Thrawn dispatched Admiral Konstantine to deal with the rebels there.

When Konstantine announced that he would depart with a full squadron, Thrawn insisted that the Admiral only deploy a single light cruiser. He reasoned that one ship would be sufficient for a man of his talents. The Admiral was unhappy but complied after Thrawn insinuated that he was not up to the challenge. Konstantine managed to damage the Iron Squadron's leader Mart Mattin and his ship Sato's Hammer and attempted to use him to lure his rebel rescuers into a trap. However, the Ghost Crew circumvented Konstantine's plan and managed to rescue Mart with the help of his uncle Commander Jun Sato. In desperation, Konstantine sent a call for reinforcements to Thrawn.

Thrawn arrived in his Star Destroyer shortly after the rebels damaged Konstantine's light cruiser. The rebels narrowly collided with his ship but managed to flee under the ventral hangar. Speaking to Sato over the com, Thrawn vowed to meet him again. The Grand Admiral replied in a similar fashion and allowed the rebels to escape. Thrawn then turned his attention to Konstantine and asked whether he had contacted him for assistance. Konstantine tried to deny it by claiming he had called to report that he had driven the rebels from the system. However, Thrawn realized that Konstantine was lying after seeing his blazing cruiser and noted that the planet's "treasonous" inhabitants had already escaped.

Hunting down Subversives
After a surge of defective vehicles at the Lothal Imperial Factory, the Imperial High Command dispatched Thrawn to investigate the presence of subversives at the factory. In fact, a small rebel cell led by the former Governor Ryder Azadi had been infiltrating the factory and sabotaging vehicles. Thrawn also initiated a new starfighter initiative to develop a TIE equipped with deflector shields. Thrawn believed that this TIE would contribute to the Empire's counter-insurgency efforts against the Rebellion.

The disillusioned Kallus leaked intelligence of the starfighter project to the Rebellion. While Kallus did not know the full details of the project, his information led the Phoenix Squadron to send Ezra, Kanan Jarrus and C1-10P to spy on the factory and link up with Ryder's cell. The rebel mission coincided with Thrawn's crackdown on the factory. After berating the workers for their poor craftsmanship, Thrawn forced the worker Morad Sumar to demonstrate how fast a 614-AvA Speeder Bike could reach maximum speed. Sumar had earlier inspected the vehicle.

The speeder bike began to overheat and Sumar begged Thrawn to end the simulation. However, Thrawn was not satisfied and set the speeder bike's engines to full speed. The faulty bike exploded and killed Sumar. Thrawn's actions horrified Ezra, Kanan, the workers, and even Kallus. Thrawn took this as an opportunity to warn the workers that they would be personally testing every vehicle they built. Thrawn then ordered Pryce, Kallus, and Lieutenant Yogar Lyste to question each of the workers. As a precaution, the Empire also jammed the factory's communication signals.

However, Ezra and his team managed to slip away and reach Section A2, which stored the blueprints for Thrawn's weapon. Meanwhile, Thrawn reassured Pryce that he had secured the chamber by ordering the sentries to shoot anyone trying to enter the facility without his personal code on sight. When Kallus expressed skepticism that Thrawn's new fighter initiative would make a difference, Thrawn responded that victory and defeat depended on the smallest details. He then ordered another worker to demonstrate his All Terrain Defense Pod. When the walker collapsed, Thrawn gestured for the Stormtroopers to arrest the man.

Thrawn later summoned Lyste and Kallus to his office. The office was decorated with holographic displays of the Ghost Crew. Thrawn then showed his subordinates one of Sabine's starbird graffiti paintings. While Lyste merely dismissed the painting as a retaining wall, the more perceptive Kallus recognized the starbird as a creature of light that had been re-appropriated as a symbol of the Rebellion. Thrawn speculated that the Ghost Crew had a special connection to Lothal.

When Thrawn inquired about their crackdown, an officer informed him that two of the workers had disappeared following his speech and that they had left behind their uniforms. Kallus advised issuing an alert but Thrawn countered that the rebel infiltrators had already found new disguises and were after his secret project. Thrawn ordered Kallus and Lyste to secure Section A2 but the rebels managed to escape the factory with the help of Kallus. Kallus allowed the rebels to escape on an AT-DP walker at the east gate's hangar bay. The rebels' escape coincided with a diversionary attack launched by Ryder at the east gate.

Reasoning that the rebel infiltrators would take advantage of the attack to make their escape, Thrawn ordered the AT-AT Pilots aboard the All Terrain Armored Transports to attack the rebel's stolen AT-DP walker. Despite the efforts of Thrawn, the rebel infiltrators managed to escape with the stolen plans. Later, Thrawn heard a report on the skirmish from Lyste. Satisfied, he dismissed him and then turned to talk with Pryce and Kallus. Thrawn voiced his suspicions that the Empire had a mole within their ranks who was supplying the Rebellion with information. When Pryce suggested questioning all Imperial personnel, Thrawn advised setting a trap for the traitor.

Strike on Lothal
Using the information stolen by Chopper, Ezra, and Kanan, Hera was able to plan a strike on the Lothal Imperial Factory. She planned to deploy a fraction of Phoenix Squadron and assigned Ezra to carry out reconnaissance work on Imperial military positions. When Sabine asked if Thrawn was there, Hera replied that there had been an increase in Imperial ships above Lothal but that they did not know for sure. Hera was forced to relieve Ezra of his duties after he experienced a Force vision of Maul and attacked a Rebel Crewman. While Ezra, Kanan, and Sabine stayed behind to deal with Maul, Hera proceeded with the mission.

Continuing the Hunt
Later, Thrawn embarked on a campaign to scour the Outer Rim for Chopper Base. Under his command, Imperial Infiltrator Droids were dispatched to Outer Rim worlds to search for the bases. One of these droids, EXD-9, stumbled upon Chopper Base and was adopted by Garazeb Orrelios and AP-5, who mistook him for a Protocol Droid. Kallus, as Fulcrum, managed to warn Zeb who disabled and reprogrammed the droid with the help of AP-5 and Chopper. The rebels then sent EXD-9 back to the Empire as an improvised bomb which destroyed a Star Destroyer.

Following the destruction of the Star Destroyer, Thrawn met with Kallus aboard the Chimaera. When Thrawn asked how the explosion happened, Kallus responded that he believed that the rebels had reprogrammed one of the Infiltrator Droids and programmed it to self-destruct back at its base. Despite the setback, Thrawn remained in good spirits because he had managed to narrow down the search for the rebel base to 94 planets.

Discovering Fulcrum
Following a meeting with sector command staff, Thrawn requested Lyste, accompanied by Kallus, to meet with him aboard the Chimaera. Once they arrived, they made their way to Thrawn's Office where Thrawn himself, was practicing hand-to-hand combat with a pair of Imperial Sentry Droids. They were, instead, greeted by Konstantine where ISB Colonel Wullf Yularen awaited them inside. The Colonel revealed himself to Kallus who instantly recognized him from his days in the academy where Yularen was a mentor. Thrawn soon follows in to inform the group that Yularen's presence is needed to extradite a rebel spy among their ranks who are feeding the Rebellion information. Yularen cautions the group on information they reveal, even to their closest allies. Thrawn then reveals that he narrowed the search for the rebel's base through analyzing rebel hyperspace routes and the planets proximity to Lothal anticipating an attack, once again. He dismisses the group to begin the investigation.

Pryce enters his office following the meeting to inquire for any progress. Thrawn states he set a trap by asserting that the rebel spy in question was present for the meeting and now they need to await for the spy to pass on the information they learned. Yularen then informs Thrawn that a coded message was beamed off the Chimaera following the transfer of Ezra, disguised as a shuttle thief who intentionally got captured prior to Lyste meeting with Thrawn to rescue Kallus, to the ship. Thrawn decided to visit the mysterious prisoner to gain a better understanding of the transmission.

Before he can do so, Kallus releases Ezra from his cell using Lyste's Code Cylinder while also informing him that Thrawn is close to discovering the rebel's base and asks Ezra to tell him where it is located. Ezra refuses to reveal it until they arrive there but Kallus reassures Ezra that he will remove the planet from Thrawn's database to hinder it's discovery. AP-5 states they can infiltrate Thrawn's office and erase the planet from the database while also gaining the clearance codes they require for Captain Rex and Kanan to retrieve them.

Upon Thrawn's arrival to the detention center, his entourage becomes suspicious with the lax security. They discover the prisoner has escaped from his cell and Yularen reveals that Lyste's cylinder was the most recent code to access the cell raising their suspicion of the Lieutenant.

The rebels manage to infiltrate the office and erase Atollon from his database but just before Thrawn returns. One of the guards informs Thrawn that Lyste is inside. With the guards at his side, Thrawn investigates his office for any tampering. Meanwhile, Kallus reactivates two of his Sentry Droids. Thrawn becomes satisfied that his office had not tampered with, however, the reactivated Sentry Droids barge in and begin attacking them, subduing his guards. Thrawn attempts to disable the droids with a clearance code, but fails to do so. While Thrawn is fighting the droids, Ezra and Chopper who were previously in hiding in the office, make their escape, but, Thrawn discovers them and mistakes the disguised Ezra as Lyste. After a brief attack, he manages to defeat the droids and informs Yularen.

The rebels make their escape, however, with Lyste being the assumed rebel spy through misinterpretation of their escape, Kallus stays behind to continue his role once Thrawn is convinced the rebel spy threat has been neutralized with Lyste as the scapegoat. While analyzing the events that unfolded, Yularen was not satisfied with how easy the conclusion was made. Thrawn agreed. They then analyzed the helmet Ezra left behind with it's depiction of a Loth-cat. Thrawn recognized the art style to belong to Sabine Wren, thus revealing to Thrawn who the shuttle thief really was. Upon learning this, they inquire why Kallus didn't report Ezra when he was captured by Lyste. Thrawn concludes that Kallus has been the rebel spy, Fulcrum, all along and in an act of deception, blamed Lyste for the crime. Thrawn then planned to manipulate Kallus into revealing the location of the rebel base.

Hunt for Mon Mothma
After Senator Mon Mothma resigned from the Imperial Senate and gave a fiery speech denouncing the Ghorman Massacre placing the blame upon Palpatine, Thrawn received intelligence that Mothma and the Ghost crew were planning to travel through the Archeon Nebula to avoid Imperial detection. Based on his knowledge of Hera, Thrawn anticipated that Hera would be risky enough to travel through the Archeon Pass. In response, he deployed his prototype TIE Defender piloted by Imperial ace, Commander Vult Skerris, and escorted by two TIE Interceptors to flush the rebels out of the nebula. Thrawn also tasked Pryce and Konstantine with positioning two Star Destroyers outside of the Archeon Nebula to capture them when Skerris drove them out. Despite Thrawn's planning, Hera and the rebels managed to escape with Mothma and her entourage following a brief skirmish in the Archeon Nebula.

Spy Droids
As part of his counter-insurgency efforts, Thrawn also utilized the services of a team of Imperial Information Office intelligence officers based aboard an Imperial Listener Ship. This team was led by Controller LT-319 and were tasked with gathering intelligence and monitoring rebel activities. As part of their intelligence operations, these spies were tasked with keeping an eye out for rebel droids such as Chopper, who had taken part in numerous undercover missions.

During the Ghost Crew's mission to Killun Station, LT-319's team detected Chopper's presence at the Imperial Security Bureau base. Using a network terminal, the team reprogrammed Chopper into a double agent droid and tried to use him to discover the location of Chopper Base. As part of the operation, Chopper hijacked the Ghost and used a Computer Spike to transfer data from the ship's navigation computer to the surveillance vessel. Before the download could be completed, the rebels retook control of their ship and removed the Imperial programming from Chopper. Hera then destroyed the surveillance vessel by sending back their data feed, causing a data surge that blew the vessel apart.

Battle of Atollon
Later, Thrawn acquired the services of several elite Death Troopers. He flew to the Imperial Complex in Lothal's Capital City for a private meeting with Pryce and Konstantine. Inside the briefing room, Thrawn closed the blinds and warned them that they still had a traitor in their midst. He also initiated a hologram conversation with Tarkin and warned that the Phoenix Squadron and General Jan Dodonna's Massassi Group were planning to attack the TIE Defender factories on Lothal. While Thrawn had not determined the location of the rebel base yet, he vowed to capture the rebel leadership alive.

Kallus was listening to Thrawn's conversation and traveled to Ezra's Tower, which had a transmitter which he had used to send his Fulcrum transmission to the rebels. However, Thrawn had followed him there. Following a fist fight, Thrawn managed to defeat the rogue ISB agent. Kallus was taken captive by two Death Troopers and brought back into the tower. Calculating the trajectory of both General Dodonna's fleet and Kallus' Fulcrum transmission, Thrawn was able to determine that the hidden rebel base was located in the uncharted Atollon System.

Thrawn ordered Konstantine to blockade the Atollon System with his Seventh Fleet, cutting off any escape with two Interdictor Cruisers. He then traveled to Atollon aboard the Chimaera with Pryce and the captive Kallus in tow. Thrawn then issued a hologram transmission to Hera, Sato, and Dodonna vowing to rain down defeat upon them. The rebel fleet tried to break the blockade but Thrawn's Star Destroyers and TIE fighters inflicted heavy casualties. The rebels only managed to find a gap in Thrawn's blockade after Konstantine disobeyed orders and went to intercept Sato's command ship, Phoenix Nest. Sato rammed his ship into Konstantine's interdictor cruiser; destroying both vessels and allowing Ezra and Chopper to flee on the Gauntlet Fighter, the Nightbrother into hyperspace.

Despite this setback, Thrawn's forces had inflicted heavy casualties on the two rebel groups. After forcing the rebels back on the ground, Thrawn ordered his fleet to bombard Chopper Base from orbit. However, the rebels had managed to activate Sabine's prototype deflector shield generator. To give the rebels the impression that their shields had stood up, Thrawn ceased the attack. He then delegated command of the Seventh Fleet to Pryce while he led the ground assault on Chopper Base. Thrawn deployed both AT-DP and AT-AT walkers for the ground assault.

In order to learn the rebels' strength, Thrawn sent his AT-DP walkers into the canyon leading to Chopper Base first. The walkers were destroyed by Rex and Zebs' detonators and a rocket launcher. However, Thrawn then deployed several AT-AT walkers. These walkers destroyed the remaining detonators, forcing the rebels to retreat. Thrawn and his Death Troopers then entered the base. The Grand Admiral also ordered his ground forces to storm the base.

One of Thrawn's AT-AT walkers managed to destroy a GR-75 Medium Transport fleeing offworld. Thrawn and his troops then surrounded Hera, Dodonna and several rebels. When Hera refused to surrender, Thrawn threaten to kill them beginning with Kanan. However, Thrawn was interrupted by the mysterious Force entity known as The Bendu, who embodied the balance in the Force. Bendu used lightning to destroy the base and strike down Thrawn's forxes. This gave the rebels the window needed to flee into space with their comrades

Undaunted by the mystical Bendu, the Grand Admiral ordered his troops to concentrate fire on Bendu, which led to him falling down to the ground effectively ending his rampage. Meanwhile, Ezra and Sabine's Mandalorian forces were able to destroy the second Interdictor Cruiser. This allowed the tattered rebel remnants to flee into hyperspace. Despite failing to capture the rebel leadership and destroy the rebel forces completely, the Battle of Atollon ended as a victory for Thrawn.

Following the battle, Thrawn confronted the fallen Bendu. When Thrawn asked Bendu what manner of creature he was, Bendu replied that he was beyond Thrawn's power to kill. The creature also predicted Thrawn's defeat, describing it as "many arms surrounding you in a cold embrace". Undaunted, Thrawn shot Bendu with his blaster. While the creature disappeared, he could still hear his laughter ringing.

Trivia

 * Thrawn originally appeared in Star Wars Legends after the original trilogy and was created by Timothy Zahn for his critically acclaimed series of books known as the "Thrawn Trilogy" which include the following books, Heir to the Empire (1991), Dark Force Rising (1992) and The Last Command (1993). His popularity with the Star Wars fanbase sparked his introduction into the Star Wars canon before the original trilogy. Zahn has approved of Thrawn's inclusion into Star Wars Rebels and is currently writing a book entitled "Thrawn", to expand upon his inclusion into the series and new canon timeline.
 * Timothy Zahn, author of the Thrawn Trilogy, has also written several other Star Wars books outside of the Thrawn trilogy, but have some reference to Thrawn or an appearance of him as well. Those include Specter of the Past (1997), Vision of the Future (1998), Fool's Bargain (1 February 2004), Survivor's Quest (2004), Outbound Flight (2006), Allegiance (2007), Choices of One (2011), Scoundrels (January 2013), 2 graphic novels involving Mara Jade, another one of Zahn's creations who was first introduced in the Thrawn trilogy and is now considered to be popular Star Wars Legends character, and multitude of short stories.
 * It should be noted that when Thrawn Trilogy was released back in the early 1990's, these books caused a resurgence in the public's interest in the Star Wars franchise for the first time since the premiere of Return of the Jedi.
 * Lars Mikkelsen, Thrawn's voice actor, is the brother of Mads Mikkelsen, who plays Galen Erso in Rogue One: A Star Wars Story.
 * Thrawn is the only Chiss to appear in the new Star Wars cannon, with Thrawn himself bringing his species back into Canon.
 * In Star Wars Legends, Thrawn gains the title of Grand Admiral after stopping a rogue Grand Admiral and taking his place, in Star Wars Rebels, he gains the rank when he stops an rebel insurgency by bombarding a planet, killing all of the rebels on the planet but along with most of the planet's population.
 * Thrawn is the second chief Star War Rebels villain to have survived an entire season, the first one being Kallus during season 1. The villains on the show who were in the original trilogy do not count.
 * The idea to bring Thrawn into Star Wars Rebels was discussed during early production of Season 1. Each of the producers suggested it to varying degrees at different times. Ultimately, Thrawn is such an important admiral that they felt it wouldn't make sense to introduce him back then: the Lothal rebel cell was just a small team with one ship on one local planet. They reasoned that Thrawn would only be brought in at a later stage when the rebellion had grown into a large enough coordinated military movement that it merited his response - essentially the same reason that they didn't introduce Darth Vader until Season Two. Their overall plan for the series was for the scale of the nascent rebellion to gradually intensify, and the Empire would react with incrementally more significant force appropriate responses.