Xeno, more famously known as Whistler, served as the astromech droid companion to Corran Horn. He shared the same R-series model designation as the renowned R2-D2.
Whistler's exterior was painted in the green and gold colors associated with CorSec, the same colors that adorned Corran's X-wing.
Whistler, an R2-series astromech droid, was initially programmed by CorSec and equipped with advanced sensors and software designed to aid in detective investigations through the analysis of case details. Corran Horn further customized Whistler by adding escape and evasion protocols.
Whistler's personality became remarkably human-like, possibly due to the advanced algorithms within his CorSec software or Corran Horn's choice to avoid memory wipes. Horn even considered the possibility that Whistler was uploading and retrieving personality data after memory wipes. Like R2-D2, Whistler even developed a sense of humor, going so far as to joke to Mirax Terrik about wanting to be Pulsar Skate's navigator once Horn retired. Whistler often acted as a self-appointed guardian for Horn, functioning almost like a brother or chaperone. After Corran Horn joined the Rogues and became withdrawn, Whistler encouraged him to socialize more with the squadron.
When Corran Horn departed from CorSec and Corellia, he brought his X-wing and Whistler with him. For two years, Corran operated under the alias Eamon Yzalli, serving as an assistant to a string of ineffective Imperial Military Prefects stationed on Garqi.
During this period, Corran frequently took his X-wing out on nighttime excursions. On one such flight, a rdava-bird was ingested by Corran's starboard engine, causing it to break. Corran contacted Lai Nootka, a Duros trader, to acquire replacement parts; however, Nootka and the crew of his vessel, the Star's Delight, were apprehended and imprisoned. The smuggled X-wing components led prefect Mosh Barris to believe that Garqi had become a center of Rebel activity. While Corran was trying to come up with a strategy to get the necessary components for his X-wing out of the hands of the guards, Whistler, using the alias Xeno, had started a "Rebel" group among students at Garqi Ag University via computer networks. However, the cell's activities were limited to vandalism with rebellious symbols and slogans. Dynba Tesc, one of the cell's members, was taken into custody after the paint she used to write an anti-Imperial slogan on the side of the Imperial court was traced back to her account. Barris was unable to obtain any useful information from her after two days of questioning, so he made the decision to have her put to death. At the same time, Corran learned that Kirtan Loor, his former Imperial Liaison Officer at CorSec, would be visiting Garqi for an inspection.
Corran created a plan to save Dynba and the crew of the Star's Delight, get his X-wing fixed in time to leave Garqi before Loor showed up, and implicate Barris in treason and the murder of "Eamon Yzalli." He suggested to Barris that instead of killing Tesc, he could let her organize an escape with her fellow Rebels and the Star's Delight crew, but sabotage the ship's shields so they could shoot it down while it was escaping, wiping out the entire cell. Corran noted that Barris could time the plan to coincide with Loor's arrival to show the Intelligence officer how effective he was at dealing with Rebels. Barris gave his approval, and Corran began to put the plan into action.
Corran approached Tesc, claiming to have changed his mind about the Empire, which had destroyed Eamon Yzalli's alleged home planet of Alderaan, and he couldn't bear to see her executed. He gave her a rank cylinder that identified her as Intelligence agent "Kirtana Loor" and allowed her to take control of the Star's Delight's crew, contact her co-conspirators, and flee. Meanwhile, he had the spare X-wing parts delivered to the Star's Delight, but he told Barris that some of the parts had been stolen, claiming that someone had taken them to fix their own T-47 landspeeder. In reality, he had taken the parts to repair his X-wing. He then instructed Barris to report that "Eamon Yzalli" had been executed for "anti-Imperial behavior" in order to get Tesc to leave without him.
The Star's Delight took off, and Mosh Barris dispatched TIE fighters to pursue it. Corran had initially intended to use the Star's Delight's escape as a diversion for his own; however, he was forced to alter his plans when he discovered that the code to activate the shields had not been given to the crew as planned. He took off after the freighter in his X-wing and gave the crew the code to turn on the shields. He destroyed all four of the attacking TIEs and fled with the ship to the Rebel Alliance.
After learning about the battle, Rebel Captain Dromath made an effort to persuade Corran to join the Alliance. Corran was hesitant at first, but he agreed to join when he learned that Rogue Squadron was being reformed and that he might be qualified to join.
Whistler also fostered a close relationship with Wedge Antilles's astromech droid, R5-G8, also known as "Gate." After Rogue Squadron was captured by Ysanne Isard, Whistler and the other astromechs were fitted with a restraining bolt and deactivated for the duration of a joint Imperial-Rogue Squadron mission to defeat Prince-Admiral Delak Krennel. Whistler, however, had been internally reconfigured during his time with Corran in the Corellian Security Force, so the restraining bolt only transmitted signals from the controller to him, rather than actually shutting him down. Whistler used his security programming to reactivate Gate, access base floor plans, and escape. The two then made reservations for passage to Oradin. Talon Karrde was reached by the pair, who then contacted Mirax Terrik through him.
During one of his missions, Corran found out that Whistler had a recorded message from his father that described his Jedi ancestry. Corran requested the droid to play the message while he was looking for his kidnapped wife, Mirax.
