John Colicos intended to reprise the role of Captain Kor in a later episode Day of the Dove (1968), but scheduling conflicts with Anne of the Thousand Days (1969) prevented this. The role of Captain Kang (Michael Ansara) was written to take the place of Kor, and the performances of both actors were so excellent that they became equally legendary.
The baldric that Kor wore was reused for Worf during the first season of Star Trek: The Next Generation (1987). When it was exhibited at the Smithsonian Institution as part of a Star Trek retrospective in the 1990s, the material could clearly be seen to be burlap sacking, painted gold. The same exhibit showed that the buckles of the Klingon belts were pieces of bubble pack, with the bubbles painted silver to resemble metal studs.
The Klingon Lieutenant played by Victor Lundin walks into the room ahead of John Colicos (Kor), making him the first Klingon to appear on screen in any Trek production, although, in a prior scene, several Klingons are seen walking through the village.
In the original broadcast, we never saw visuals of the Klingon vessels either on the view screen or on exterior shots, just explosions on the view screen where the Klingon vessels were supposed to be. In the "Remastered" release (2006), new shots of the D7 Klingon Battle Cruisers, designed and built by art director Walter M. Jefferies, were digitally inserted into various shots, providing new visuals of the Klingon ships that were not present before. Due to this addition, this would now officially make this the first episode of the series to feature the D7s. Originally, the D7s did not appear until the Third Season of the series and the original first episodes to feature them were The Enterprise Incident (1968) and Elaan of Troyius (1968), which were aired in reverse order from when they were filmed.