Kubus Oak was a Bajoran official during the Occupation of Bajor, serving as Secretary of the Bajoran Occupational Government and liaison to the Cardassian Union. His duties included signing off on Cardassian orders for new Bajoran mine laborers. Though the orders were effectively death sentences, Kubus never once refused to authorize them. He rationalized his actions with the belief that the Occupation would have been far worse without him and others in the Occupational Government.
When the Occupation ended in 2369, Kubus left with the Cardassians and retired on Cardassia Prime. In absentia, he and other Bajoran collaborators were exiled from Bajor by the Ilvian Proclamation, on which Kubus's name was listed fourth.
In 2370, Kubus arrived at Deep Space 9, hoping to spend his remaining days on Bajor. He was quickly recognized and arrested by Chief of Security Odo. After Major Kira Nerys denied his request to return to Bajor, he contacted Vedek Winn Adami and gave her circumstantial evidence that Vedek Bareil Antos, not Prylar Bek, was the traitor responsible for the Kendra Valley Massacre. Wanting to use the information against Bareil in the upcoming election for kai, Winn granted Kubus sanctuary on Bajor. (DS9: "The Collaborator")
The character of Kubus was different in the story idea that Gary Holland pitched to Ira Steven Behr, Robert Hewitt Wolfe and Peter Allan Fields on 1 February 1994. Holland commented, "In my pitch, the Bajoran who later became secretary Kubus Oak, was trying to return to his homeworld, but Kira found out there was more to the man than met the eye. The twist was that Kubus had something to do with murdering Kira's father. But as we went along through the story's twists and turns we would learn that the murderer was one of Kubus' children, for whom he was covering up." Ira Steven Behr suggested that Kubus be a collaborator and the idea of Kira's father having been murdered by Kubus' daughter was dropped. (The Official Star Trek: Deep Space Nine Magazine issue 9; Star Trek: Deep Space Nine Companion)
Kubus Oak was played by actor Bert Remsen. Kira actress Nana Visitor once remarked that he was "so good" at portraying Kubus. (The Official Star Trek: Deep Space Nine Magazine issue 16, p. 48)