On American television, he established himself as a science-fiction villain icon, portraying the first Klingon ever seen in the "Star Trek" franchise, Commander Kor in the ' episode "Errand of Mercy" (1967). Colicos worked with Gene Roddenberry designing the look the Klingons have on Star Trek (1966). Budget constraints prevented the extensive makeup the Klingons were supposed to have so Colicos suggested they have a leathery Genghis Khan look, dark skin and hair. He also portrayed Count Baltar in the original "Battlestar Galactica" movie and television series. Over a quarter-century after his initial appearance in the "Star Trek" franchise, Colicos reprised his role as the 140-year-old Kor in three episodes of ', telecast between 1994 and 1998.