The show’s pilot was called “The Cage” and had a copyright date of 1964.
“The Cage” was filmed at Desilu Productions’ studio (now known as Culver Studios) in Culver City, California, from November 27 to mid-December 1964.
Post-production work (pick-up shots, editing, scoring, special photographic and sound effects) continued to January 18, 1965.
According to Wikipedia, “The Cage” had many of the features of the eventual series, but there were numerous differences. The Captain of the starship USS Enterprise was not James T. Kirk, but Christopher Pike (played by Jeffrey Hunter).”
Spock was present, but not as First Officer. That role was taken by a character known only as Number One, played by Majel Barrett.
Spock was played by Leonard Nimoy and had the first line in all of Star Trek: “Check the circuit!” followed by, “Can’t be the screen then.”
Susan Oliver played the part of Star Trek’s original Orion Green Girl, part of her role as “Vina” in the original 1964 pilot.
NBC reportedly called the pilot “too cerebral,” “too intellectual,” and “too slow” with “not enough action.” Sources claim it was also too sexy.
Rather than rejecting the series outright, though, the network commissioned—in an unusual, and at the time unprecedented, move—a second pilot. This was accepted and Star Trek: The Original Series began production.
Footage from “The Cage” was also “recycled” and used in a show called “The Menagerie” during the first season.