Koval was the chairman of the Romulan Tal Shiar during the Dominion War. He was a long-standing opponent of the Federation–Romulan Alliance, advocating that the Romulan Star Empire should seek a separate peace with the Dominion. This outspoken stance was believed to be the reason he had not been elevated to the Continuing Committee, as is usually the case for the chairman of the Tal Shiar. Koval often stated that there was a Federation spy in the Romulan Senate.
In that year, Koval attended a conference between the Federation and the Romulan Empire on Romulus. He approached Julian Bashir and asked him if the Quickening virus could be replicated and later attended a lecture that Bashir gave about the disease. It was at the lecture that Bashir noticed Koval's displaced eyelids, weakness in his facial muscles and irregular respiration. Bashir concluded that Koval was suffering from the early stages of Tuvan syndrome.
Later, and stalling for time while he believed Luther Sloan was going to assassinate Koval, Bashir was given a microcellular adhesive to gain a skin sample from him, which could prove whether or not Koval had Tuvan syndrome. Bashir got the sample, but was detained and interrogated by Koval.
Koval later appeared before the Continuing Committee and told them that Section 31 did not exist, and that it had been fabricated by Sloan to seek revenge on Koval for the death of Fujisaki, without implicating the Federation as a whole.
After finishing delivering his findings to Praetor Neral, the Romulan leader told Sloan that he would be detained by the Tal Shiar. Sloan suddenly reached for a disruptor of a Romulan guard but was apparently vaporized by Koval.
William Ross later revealed to Bashir that Koval was a Federation operative and had been working with Starfleet Intelligence for more than a year. He was unaware of how long the Romulans had been working with Section 31. The "assassination plot" was in actuality a collaborative effort between Starfleet, Section 31 and Koval himself to ensure Kimara Cretak's dismissal from the Senate and that he would get his placement on the Continuing Committee instead of her. Koval's previous record of opposing the Federation Alliance would then serve to reinforce his arguments to keep the alliance intact. Koval's placement gave the Federation an ally inside the highest reaches of the Romulan government. (DS9: "Inter Arma Enim Silent Leges")
- The script of "Inter Arma Enim Silent Leges" described Koval in the following way: "Koval is a heavy-set Romulan wearing the black tunic of the Tal Shiar, with a lot of iron-gray in his hair. His deeply lined face looks like it would shatter into pieces if he attempted a smile."
- It seems likely that Koval's interrogation of Bashir was staged and that he knew from the outset that Bashir's genetically engineered status would prevent any lasting neural damage. Also, it seems that Koval's interest in the Quickening was designed to stop Bashir from trying to help save his life.
- Koval was played by John Fleck, in his fourth Star Trek appearance. His first was in TNG: "The Mind's Eye", where he played another Romulan, Taibak. His two previous DS9 appearances came in DS9: "The Homecoming" as a Cardassian officer and DS9: "The Search, Part I" as the Karemma First Minister Ornithar. He later guest-starred in VOY: "Alice" before taking on the recurring role of Silik in Star Trek: Enterprise.
- Koval is revealed to have been assassinated in the Star Trek: Titan novel Taking Wing.
- In the short story, "Suicide Note" by Geoff Trowbridge (which was printed in The Sky's the Limit), Koval is referred to as a general officer in the Tal Shiar leading the interrogation of Admiral Alidar Jarok's wife and daughter after his defection (in TNG: "The Defector"). Jarok's farewell message reveals that Koval is actually one of Jarok's sympathizers, who opposes the Empire's militarism and promises to keep Jarok's wife and daughter safe after his departure. Captain Picard reactivates Koval as an agent for Federation Intelligence when he visits Romulus to deliver Jarok's farewell message, by which time Koval has risen to the chairmanship of the Tal Shiar.