In DS9's seventh season episode "Once More Unto The Breach", Kor has lost most of his influence in the Klingon Empire and feels out of place in the conflict against the Dominion. He turns to Worf to help him find a command so that he might have the opportunity to fight and die as a warrior, though General Martok, who had once been shunned from the Klingon Defence Force by Kor, was hesitant to allow the Dahar master any kind of position in his fleet. Worf, however, was able to find Kor a position aboard the IKS Ch'Tang using his own authority, and so Kor was appointed Third Officer of that vessel.
During a raid on the Dominion base on Trelka V, Kor took command when Martok was injured, but it became clear that age was taking its toll on Kor as he began to relive an old battle against the Federation from long before the Federation and the Klingons had joined forces. With Kor losing his grip on reality, the Ch'Tang was in serious danger and Worf knocked him out before ordering an escape course.
After his senile episode, Kor was ridiculed by Martok and the Ch'Tang crew. Later, the Bird-of-Prey was pursued by a small fleet of Jem'Hadar fighters and Worf had devised a strategy to delay them before the Klingon squadron rendezvoused with the USS Defiant. The plan was sound, but Kor, having been informed of the plan by Martok's aide Darok, did not believe that Worf was experienced enough to carry it out. Before Worf transferred to the IKS Ning'Tao, Kor surprised him outside the transporter room with a hypospray and took his place on the Ning'Tao.
Kor's death was not shown on-screen, nor was any part of his skirmish with the Jem'Hadar, but the Ch'Tang monitored his progress as long as they could and he had successfully fended off the ten enemy vessels with just one ship and six volunteers. General Martok and his crew toasted Kor for his courage and heroism.