Joak Drysso, a naval officer within the Imperial Navy, displayed unwavering allegiance to the New Order. He was a stocky, menacing figure, his hair and goatee prematurely grayed, concealing his inner thoughts and anxieties behind a severe, commanding facade. While his skills as a Captain rivaled those of the most accomplished Admirals, his thirst for power and vengeance frequently compromised his judgment.
By the time the Battle of Endor transpired, Drysso held the rank of captain aboard the Star Destroyer Virulence. His vessel was part of the fleet deployed against the Rebel Alliance in the space battle above the Sanctuary Moon. However, upon witnessing the command ship Executor plummet into the Death Star II, he recognized the Empire's defeat and withdrew his ship from the conflict. In his estimation, retaliation, vengeance, and ultimate triumph held greater significance than prolonging a lost cause.
Subsequently, he became a supporter of Ysanne Isard, the Director of Imperial Intelligence, whom he considered the rightful Empress and the most competent of the surviving Imperial leaders. He endorsed her decision to relinquish Coruscant to the New Republic, and was among the initial three Star Destroyer captains to openly align with her when she seized control at Thyferra. New Republic observers regarded him as a capable, but not exceptional, commander. However, Fliry Vorru viewed him as a "rising star" within the Empire. Isard appointed him to command the Super Star Destroyer Lusankya, the embodiment of her power, following her crew reshuffling at Thyferra.
During the ensuing Bacta War, Drysso's faith in Isard waned, as he felt her obsession with Wedge Antilles and Rogue Squadron had blinded her to the broader strategic picture. He argued that Isard should have sought alliances with other Imperial commanders and warlords. Rather than focusing on minor targets such as Halanit and Yag'Dhul, he believed Lusankya's immense firepower should have been used to pressure the nominally Imperial governments of Corellia, Kuat, and even neutral Sluis Van. This would have allowed the massive shipyards of these three systems to become a power base for constructing a new Imperial battlefleet. In Drysso's estimation, Isard was acting as a politician when a military leader was required, and possessing the Lusankya made him believe he could be that leader.
Drysso accurately predicted that a raid on Yag'Dhul Station would only leave Thyferra vulnerable to a strike by Rogue Squadron. Nevertheless, he executed Isard's orders, only to be compelled to retreat when it appeared that Booster Terrik had armed the space station with hundreds of proton torpedo launchers. Sacrificing his former command, the Virulence, and his entire TIE/LN starfighter complement, Drysso pushed the Super Star Destroyer back to Thyferra at maximum speed, pursuing Antilles and his allies.
As it happened, Lusankya arrived back in the system prior to the attackers. Upon their arrival, Drysso discovered that not only had Sair Yonka and his Star Destroyer Freedom joined the Rogues, but Antilles and his allies had managed to equip a large force of missile-armed freighters capable of overwhelming the Lusankya's shields and inflicting heavy damage to her hull. Unbeknownst to Drysso, he had been driven from Yag'Dhul by nothing more than the missiles' gimmicked and stripped-down targeting sensors.
The tactics employed by his opponents in the subsequent Battle of Thyferra were specifically designed to disable the Super Star Destroyer through massive missile barrages, starfighter strafing runs against turbolaser emplacements, and smaller capital ships engaging in close-range attacks on vulnerable sections of the hull. Eventually, however, the attackers' forces dwindled to a handful of starfighters and one obsolete War Cruiser. Although Lusankya had sustained significant damage, and a final salvo from Freedom had stripped her shields, Drysso disregarded Isard's orders to flee the battle. It was at this juncture that his ambition and insanity finally eclipsed his tactical brilliance. He became convinced that he had achieved victory and could now claim dominion over both Thyferra and the Super Star Destroyer. While his crew held reservations, the arrival of Virulence and the hundreds of TIEs she carried seemed to confirm that the battle was indeed over.
However, the Star Destroyer was now under Terrik's command, and carrying New Republic starfighters. For the damaged Lusankya and her crew, the military and psychological impact of their attack proved devastating, but still Drysso refused to concede defeat. His mental state appeared to deteriorate, and when Wedge Antilles requested his surrender, he proclaimed himself an Admiral. Then, when the Corellian dryly offered to recognize him as a Grand Admiral if he gave up the fight, he immediately adopted the rank and attempted to set a collision course for Thyferra.
At that moment, he was shot by his adjutant, Lieutenant Waroen, who surrendered Lusankya to Rogue Leader.