Star Trek's first pilot "The Cage" is the only episode of the original series to not feature Bill Shatner - and it arguably suffers for it, lacking energy and humor.
During Star Trek's first season, Gene Roddenberry devised a way to re-use, by means of flashback sequences, footage from that never-broadcast pilot in two new episodes. Helping to ease broadcast deadlines, only a limited number of new scenes would be combined with that existing footage. A unique opportunity was thus created to add the dynamics of both Bill Shatner and his toupee into "The Cage" in a new two-part episode called "The Menagerie".
Through shot composition, director Marc Daniels frequently used the toupee to give clues about the themes in "The Menagerie".
We've occasionally said that Star Trek owes much of its initial dramatic success to Bill Shatner's toupee and "The Menagerie" is but one example of the inspiration that the toup gave both writers and directors. Marc Daniels, who directed the new material for "The Menagerie" only needed one look at the toup to understand that this was a two-parter all about illusions versus reality. The way that Daniels framed shots featuring actor Malachi Throne (whose baldness mirrored Bill Shatner's), alias Commodore Mendez, and Bill Shatner helped to underline this concept.
One actor was wearing a toupee, the other represented Bill Shatner toup-less. We later learn that Mendez was an illusion created by the Talosians (who had giant bald heads) - interestingly, Throne also provided the dubbed voice for the lead Talosian (his voice was pitch-shifted upwards in "The Menagerie" to differentiate it from the character of Mendez - scroll down this page to hear the difference).
At the end of the episode, the Talosian tells Kirk "Captain Pike has an illusion, and you have reality; may you find your way as pleasant." The concept is reversed - in reality, Shatner has the illusion, while Kirk has the reality (the character's hair is real). Bill Shatner's toupee is only now gradually gaining its rightful recognition as one of the chief creative inspirations in Star Trek - may that recognition continue to grow.