Klingon officer who was the military governor of the planet Organia during the border dispute in 2267.
Kor ruled Organia with an iron fist, but was unaware that the apparently humanoid Organians were in fact incredibly advanced noncorporeal life forms who sought only to promote peace between the two antagonists. (Errand of Mercy [TOS])
NOTES: Years after Colicos' appearance as the first Klingon on Star Trek, the actor reprised his role of Kor in "Blood Oath" [DS9].
Along with Kor, that episode featured appearances by Michael Ansara as Kang and William Campbell as Koloth.
All three actors wore bumpy foreheads for "Blood Oath", thereby raising a question of whether these were the same characters, or merely other Klingons with the same names.
Actor John Colicos also played Lord Baltar on Battlestar Galactica.