(written from a Production point of view)
Joseph "Joe" D'Agosta was the casting director of Star Trek: The Original Series during its entire three-season run, starting with the second pilot, "Where No Man Has Gone Before" (after producer Herb Solow decided to hire a professional casting director, feeling that several parts had been miscast in "The Cage"). He was also the casting director of Mission: Impossible and The Lucy Show at the same time, which were all produced by Desilu. D'Agosta started out as an actor, but very soon turned to casting.
During his career in casting, spanning more than four decades, D'Agosta worked on both television and film. His credits include Gene Roddenberry's series, The Lieutenant, which starred Gary Lockwood, Mannix and The Brady Bunch, and films such as Poltergeist II: The Other Side (1986). D'Agosta is the husband of actress Barbara Baldavin, whom he cast as Angela Martine in "Balance of Terror", "Shore Leave", and "Space Seed", and as Lisa in "Turnabout Intruder". Sean Morgan, a regular bit player on Star Trek was a college friend of D'Agosta, which lead to him being cast in smaller roles on the series. He was also a classmate of Ralph Maurer at acting school, and cast him in two episodes of Star Trek.