"Turnabout Intruder," to be honest, isn't necessarily an episode to be celebrated. Far from the finest hour of Star Trek: The Original Series, it's little more than yet another a mad scientist tale. However, it holds one particular distinction, which is why we're going to share some details, facts and figures about "Turnabout Intruder," and that distinction is this: it aired on June 3, 1969, 46 years ago today, and turned out to be the last-ever TOS episode.

Gene Roddenberry wrote the story outline for "Turnabout Intruder"... way back in April of 1968.

Herbert Wallerstein directed "Turnabout Intruder" after having previously put the cast and crew through their paces for "The Tholian Web," "That Which Survives" and "Whom Gods Destroy." Sadly, Wallerstein died in 1985 at the age of 59, having been beaten to death by his housekeeper, who claimed she was defending herself.
Roger Holloway played Lemli, which is memorable for a couple of reasons. First, he'd played the Starfleet crewman many times before... but without a character name or any dialogue. He uttered two words in the series finale and received the name Lemli. William Shatner's licence plate at the time read LEMLI -- a mix of his daughters' names: Leslie, Melanie and Lisabeth -- and to this day his production company is called Lemli Productions.
Nichelle Nichols does not appear in the episode.
Jeffrey Hunter, the original choice for captain of the Enterprise, who beamed away from Star Trek after shooting "The Cage," died on May 27, 1969, a week before "Turnabout Intruder" premiered. Just imagine how different Star Trek might have been if he'd continued to play Captain Pike. Would there ever have been TOS movies or spinoffs?
The very last day of filming was January 9, 1969.
"Turnabout Intruder" was supposed to air on March 28, 1969. However, former President Dwight D. Eisenhower had died, prompting NBC to bump the episode... to June.
Captain Picard, in the Next Generation episode "Legacy," notes that the Enterprise is bypassing an archeological survey on Camus II, precisely where the action in "Turnabout Intruder" commences. That was TNG's tip of the cap to TOS, as it marked the 80th episode of TNG, surpassing TOS, which ended after 79 episodes.
Sandra Smith, who played Dr. Janice Lester and also Captain Kirk in the episode, will turn 75 years old later this month, on June 27.
William Shatner
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Jeffrey Hunter