Kupalo was a male Human tactical officer serving the Rebel cause. During the Battle of Hoth, he was captured and subsequently subjected to brainwashing, transforming him into an Imperial agent working against his former allies.
Prior to the Battle of Hoth, Kupalo held the rank of Commander and served as Tactical Officer aboard the Mon Calamari Star Cruiser Defiance, under the command of Admiral Nammo. He was well-regarded as a highly skilled and competent officer, earning his superior's respect. During the devastating Rebel defeat on Hoth, Kupalo was present on the planet's surface. Unable to escape, he was captured by the invading Imperial forces.
Recognizing Kupalo's position within the Alliance, the Empire devised a scheme to infiltrate a highly placed operative into the growing revolutionary movement. Kupalo was subjected to extensive Imperial 'conditioning', a process that not only instilled unwavering obedience and loyalty to the Empire in its victims, but also left them as "empty shells of their former selves".
The challenge for the Empire was to return the newly turned double agent to his former position within the Alliance without raising suspicion. Their solution was straightforward yet effective. They intentionally leaked information about an Imperial Dreadnaught prisoner transport, VTR-LX, en route to a penal station carrying Rebel prisoners of war. The Dreadnaught and its escort vessels, Assault Gunboats from Tau Squadron and Delta-class JV-7 escort shuttles from Manticore Squadron, made a stop at a civilian spaceport for refueling, presenting the Rebels with an opportunity to strike.
As the Dreadnaught completed refueling at Calast space station, X-Wings from Red Squadron, including pilot Ace Azzameen, and Y-Wings from Green Squadron emerged from hyperspace. While the Rebel fighters successfully destroyed the Gunboats, the Dreadnaught and Escort Shuttles managed to escape into hyperspace with the POWs. Thanks to the quick thinking of Tactical Officer Commander Devers, the Rebels were able to identify the only penal station along the Dreadnaught's hyper vector: the XQ2 Platform orbiting Bundil II.
The fighters pursued at high speed, arriving almost simultaneously with the Dreadnaught. Red Squadron swiftly eliminated the Escort Shuttles and engaged the TIE Fighters launched from the platform's hangars, while Green Squadron focused on disabling the Dreadnaught as ordered. After its shields finally collapsed, a relentless ion cannon barrage from the Y-Wings crippled the Dreadnaught, enabling a boarding action.
The effectively defenseless Dreadnaught was unable to prevent the assault transport carrying elite commandos from Storm Unit from boarding the disabled vessel. Under the cover of the fighters battling attacking TIEs, the commandos successfully rescued the POWs and returned to the Defiance. Unbeknownst to the Rebels, their most valuable prize was actually a secret weapon for the Empire.
With the Mon Calamari Cruiser Liberty assigned to investigate the shipping attacks in the Vilonis sector, Ace Azzameen's Squadron was reassigned to the capital ship to replace crewmembers lost in a recent battle. The ship also required a new Tactical Officer, creating the ideal opportunity for the newly recovered commander. Together, the Liberty and its new personnel successfully thwarted the TIE Experimental Project.
Kupalo's time in this role was short-lived. The Liberty's next mission involved extracting an Imperial defector, Commander Zaletta. Kupalo carefully timed his move. Exploiting the Rebel forces' celebratory mood, Kupalo summoned the Imperial II-class Star Destroyer Subjugator and the Interdictor Cruiser Restrainer, hoping to swiftly and decisively destroy the Nebulon-B Frigate Redemption, Zaletta, and potentially even the Liberty. It's also possible that, given Zaletta's extensive knowledge of classified Imperial projects (including information regarding the construction of the Death Star II), he might have known about Kupalo's collaboration with the Empire, leading Kupalo to want to eliminate him; however, this is purely speculative.
Despite the valiant efforts of the starfighter pilots and the crews of the Liberty and Redemption, the ambush failed, and the Rebels managed to escape. Kupalo temporarily shifted blame onto Zaletta, but he knew his deception wouldn't last. Realizing he needed to escape and invalidate Zaletta's defection, he decided to steal Zaletta's shuttle, AA-23, which contained all the information Zaletta had provided to the Alliance. After blasting his way out of the hangar bay, Kupalo planted charges that severely damaged the hangar, rendering it unusable for some time. He evaded three pursuing X-Wings by deploying homing mines from a concealed compartment on the shuttle's underside, destroying them, and then jumped to hyperspace.
Anticipating multiple jumps to evade pursuit, Ace Azzameen and his wingmate Olin Garn were dispatched in A-Wings to intercept him. They caught up with him at his first exit point and, despite facing a group of Gunboats and another barrage of homing mines, they managed to damage his engines and force him to surrender. Kupalo, however, had one more trick up his sleeve. He signaled the Star Destroyer Imperator, hoping for rescue. In a display of exceptional bravery, Garn and Azzameen single-handedly destroyed a large number of attacking TIE Starfighters, preventing them from reaching the shuttle and the Assault Transport sent to retrieve it. Kupalo was brought back to the Liberty, where he was imprisoned and treated, with Commander Zaletta replacing him in his duties.
As Admiral Yamarus, the commanding officer of the Liberty, stated, it was uncertain whether Kupalo ever fully recovered from his ordeal.