For those racking their brains, Kras was the Klingon in "Friday's Child", played by Tige Andrews.
Possibly. Apparently Andrews was approached to be the main Klingon in "Trouble with Tribbles", but couldn't do it due to other commitments, so William Campbell got it instead. Other trivia: Andrews got the Kras job due to Shatner recommending him to the casting supervisor. It was his first sci-fi role, and he had a lot of fun with the part.