O'Reilly made his first appearance in the "Star Trek" franchise with an appearance in the "" episode "". The character he played in that episode has been referred to both as "Tough guy" and "Scarface". He was then cast as the Klingon Gowron in the episode "" which saw the character become the new Chancellor of the Klingon Empire. O'Reilly had just finished appearing on stage as Edmund in "King Lear" and saw similarities between the two characters which resulted in him basing Gowron upon the Shakespearian character. The episode was directed by "TNG" cast member Jonathan Frakes, and O'Reilly later said that he thought he was hired both for the sense of curiosity he brought to the role and a piercing, unsettling gaze he and others referred to as "that crazy loon eyeball thing".