"Star Trek: The Original Series" aired 79 episodes. The series debuted on Sept. 8, 1966 with the episode "The Man Trap." The show was almost cancelled after the second season, but a letter-writing campaign by fans saved it. The final episode, "Turnabout Intruder," aired on June 3, 1969.
Creator Gene Roddenberry filmed the first pilot, "The Cage," in December 1964. NBC rejected the show as too cerebral but allowed Roddenberry to film a second pilot with new characters, "Where No Man Has Gone Before," which became the fourth episode. Footage from original pilot was repurposed as flashbacks in the two-part episode, "The Menagerie."
After its cancellation, "Star Trek: The Original Series" spawned an animated series, four more live-action series and 12 movies. J.J. Abrams re-imagined the original series characters and timeline for his movie "Star Trek" in 2009, launching a new series of movies.