Even as the first season was being filmed, Roddenberry was flirting with the idea of a younger man joining the Enterprise crew in order to beef up the show’s teen appeal. He took note of Brad Weston (pictured here as Appel in “The Devil In The Dark”) for this role, sending a memo to casting director Joe D'Agosta that read:
In “The Devil In The Dark” I saw a young “Fess Parker” type character; I think his name was Weston… who was sort of a second in command of the miners…with the heavy set of hair. I’m interested in him; can we talk about his background and ability?
Walter Koenig eventually got the role that Weston had been eyed for.