Warden of Rura Penthe
A klingon, the Warden was in charge of the frozen wasteland/gulag, Rura Penthe. Arguably, the most noteworthy prisioners under his tenure were Kirk and McCoy, when the two Starfleet officers were falsely imprisioned for the murder of Chancellor Gorkon. The Warden interrupted a fist fight between Kirk and Martia -- a shape-shifter posing as Kirk -- by killing Martia.
Apparently somewhat informed of the conspiracy bent on disrupting Klingon-Federation peace talks, the Warden was about to reveal names of key conspirators to Kirk when the captain and Dr. McCoy were safely beamed aboard Enterprise.