Joak Drysso was an officer in the Imperial Navy, and a staunch New Order loyalist—a squat, dangerous looking man whose hair and goatee turned gray early, and who hid his thoughts and worries behind a stern mask of command. His skill as a Captain rivalled that of the most competent Admirals, though his desire for power and vengeance often proved to impede his judgement.
By the time of the Battle of Endor, Drysso was captain of the Star Destroyer Virulence, and his command was part of the fleet deployed against the Rebel Alliance in the battle above the Sanctuary Moon. When he saw the command ship Executor crash into the Death Star II, however, he realized that the Empire had lost the battle, and withdrew his own ship from the fight. From his perspective, striking back and achieving vengeance and ultimate victory was more important than fighting a losing battle.
Subsequently, he became a supporter of Ysanne Isard, the Director of Imperial Intelligence, who he regarded as the rightful Empress, and also as the most capable of the surviving Imperial leaders. He supported her decision to cede Coruscant to the New Republic, and he was one of three Star Destroyer captains who joined her openly when she seized power at Thyferra. He was seen as a capable but not outstanding commander by well-informed observers in the New Republic, but Fliry Vorru considered him a "rising star" within the Empire, and he was appointed by Isard to command the Super Star Destroyer Lusankya, the embodiment of her power following her reshuffling the crew at Thyferra.
During the subsequent Bacta War, however, Drysso became disillusioned with Isard, musing that her obsession with Wedge Antilles and Rogue Squadron had blinded her to the wider response. He believed that Isard should have negotiated an alliance with other Imperial commanders and warlords, and that rather than concentrating on small targets like Halanit and Yag'Dhul, Lusankyas massive firepower ought to have been employed to coerce the nominally Imperial governments of Corellia, Kuat and even neutral Sluis Van, so the massive shipyards of these three systems could thus have become a powerbase to build a new Imperial battlefleet. In Joak Drysso's view, Isard was a politician where a military leader was needed, and now that he had Lusankya he was starting to believe that he could be that man.
Drysso correctly predicted that a raid on Yag'Dhul Station would only expose Thyferra to a strike by Rogue Squadron, but he nevertheless carried out Isard's orders, only to be forced to flee when it seemed that Booster Terrik had armed the space station with hundreds of proton torpedo launchers. Sacrificing his former command, the Virulence, and the entirety of his TIE/LN starfighter complement, Drysso raced the Super Star Destroyer back to Thyferra at flank speed, in pursuit of Antilles and his allies.
In the event, Lusankya arrived back in the system before the attackers, and when they appeared, Drysso discovered that not only had Sair Yonka and his Star Destroyer Freedom joined the Rogues, but Antilles and his allies had been able to equip a massive force of missile-armed freighters which could overpower the Lusankyas shields and savage her hull. Although Drysso never knew it, he had been driven away from Yag'Dhul by nothing more than these missiles' gimmicked and stripped-down targeting sensors.
His opponents' tactics in the subsequent Battle of Thyferra were designed specifically to take down the Super Star Destroyer with massive missile attacks, starfighters performing strafing runs against turbolaser emplacements, and smaller capital ships moving in for close-range attacks on vulnerable sections of the hull. Eventually, however, the attackers' effective forces were reduced to a few starfighters and one obsolescent War Cruiser. Although Lusankya herself had sustained serious damage, and a final salvo from Freedom stripped her of her shields, Drysso scorned Isard's orders for him to flee the battle. It was here that his ambition and madness finally outweighed his tactical genius. He believed that he had won, and could now claim mastery of both Thyferra and the Super Star Destroyer. His crew were less certain, but the arrival of Virulence and the hundreds of TIEs she was carrying seemed to indicate that the battle really was 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 mind appears to have become somewhat unhinged, and when Wedge Antilles asked him to surrender, he declared 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 this point, he was shot by his adjutant, Lieutenant Waroen, who surrendered Lusankya to Rogue Leader.
- The Complete Star Wars Encyclopedia