Trivia

After the pilot aired, the studio told Gene Roddenberry to get rid of the guy with the ears, Mr. Spock. But Roddenberry wanted an alien presence on the bridge and had to fight to keep the character.

Leonard Nimoy's Mr. Spock was the only character from the first pilot retained into the series. The ship's first officer character, Number One, was rejected for the series by the network because she was female (according to Gene Roddenberry), or because of her lack of acting ability (according to Desilu production chief Herbert F. Solow). Actress Majel Barrett (Roddenberry's girlfriend at the time and later wife) was recast as Nurse Chapel. When the pilot was recycled as The Menagerie: Part I (1966) and The Menagerie: Part II (1966), it was established that Captain Pike's voyage to Talos IV took place 13 years prior to the events of the Star Trek (1966) series.

The original script called for the aliens to be crab-like arthropods. Since the budget would not allow this, they were made into humanoids with bulging brains, beginning a Star Trek tradition of almost all aliens being of a shape that could be easily played by human actors.

The first pilot was not aired on TV until 1988, when it was used as a filler episode for Star Trek: The Next Generation (1987) due to a writers strike.

NBC reportedly called the pilot "too cerebral", "too intellectual", and "too slow" with "not enough action." Rather than rejecting the series outright, the network commissioned - in an unusual, and at the time unprecedented, move - a second pilot, which then became Where No Man Has Gone Before (1966). This was accepted and Star Trek: The Original Series began production.