Doctor Parmak is a Cardassian whom Garak once broke under interrogation simply by sitting and staring at him for hours, an episode recalled when Garak is reunited with Enabran Tain.
Parmak is mentioned in the third-season episode The Die Is Cast and does not appear. Aboard Tain's warbird, as Garak settles back into his old role in the Obsidian Order, the two men reminisce about past interrogations, and the case of Doctor Parmak is held up as an example of Garak's skill.
As the story is told, Garak never laid a hand on the man. He sat down opposite him and looked at him steadily for about four hours, until Parmak broke down and confessed everything.
The anecdote sets up the episode's grim reversal, in which Garak is required to interrogate Odo and finds that he no longer has the stomach for the work. Parmak is developed further in the novel A Stitch in Time, which lies outside screen canon.