In June 1964, NBC approved the production of the 1st Star Trek pilot story "The Cage". Ofcourse, that pilot did not result in the commissioning of a new television series; but the studio did take the unprecedented step of ordering a 2nd pilot - "Where No Man Has Gone Before". The second attempt featured William Shatner as Captain James T. Kirk, replacing the character of Captain Christopher Pike that had been played by Jeffrey Hunter in "The Cage", and this pilot did lead to the 3 seasons of TOS. Jeffery Hunter was offered the opportunity to reprise his role in the second pilot; but declined so that he could pursue motion picture work instead of television. The first pilot was eventually integrated into the first season broadcasts as the only two-part episode of Star Trek, called "The Menagerie".
And now for some rare photographs taken behind the scenes during "The Cage" production ...