Darok was a Klingon who served aboard the IKS Ch'Tang in 2375. He was the elderly aide of Martok. Darok befriended Kor, despite his collapsing mental capacity, because he reminded him of a Qo'noS that once was.
Martok often belittled Darok, for being elderly instead of having died with honor, while Worf referred to him as a shuVak who existed merely to be "ordered about". Martok would further tell Darok that one day "his services would no longer be required", hinting that he might have him executed, to which Darok would reply that he looked forward to that day with great anticipation.
When the Ch'Tang was being pursued by a small fleet of Jem'Hadar attack ships, Darok brought Kor the news, and confided that Worf was planning to lead a suicide attack with a small force of volunteers aboard the IKS Ning'tao in a delaying action, to allow the rest of the Klingon fleet to reach safety. He reminded Kor that it would take great tactical experience to successfully delay the Jem'Hadar, which encouraged Kor to knock Worf out and take his place aboard the doomed ship.
While the Ch'Tang's bridge crew monitored the progress of the attack, Darok brought a bottle of bloodwine onto the bridge, in defiance of regulations. He told Martok that whether they succeeded or failed, Martok could still toast their courage. When Kor succeeded in saving the fleet, at the cost of his own life, Martok passed around the bottle and Darok led the bridge crew in a song to honor the fallen Dahar Master. (DS9: "Once More Unto the Breach")