Leonard Nimoy hosted a 1975 TV special of Star Trek's The Original Series' "The Menagerie", and the rare footage has resurfaced on YouTube. In 1964, Gene Roddenberry produced "The Cage," the original hourlong pilot for Star Trek. NBC rejected "The Cage" but commissioned a second Star Trek pilot, with the entire show recast except for Leonard Nimoy's Vulcan Mr. Spock. In Star Trek: The Original Series season 1, "The Cage" was refashioned into a two-part episode, "The Menagerie," that showed nearly all of Star Trek's original pilot as a flashback.
https://screenrant.com/star-trek-menagerie-original-pilot-movie-leonard-nimoy/