Is Spock the main character of TOS (sans Abrams reboot)? Here are some facts to support this idea:
1. Spock is the only TOS character whose immediate family we see and get to know with any depth (we do see Kirk’s (dead )brother, sister-in-law, and nephew in one episode, Kirk's son in ST:II (thank you Nerys Myk
for reminding me!) and McCoy’s father is briefly seen in ST: V).
2. Spock is the only character we see throughout all stages of life; birth, childhood, early adulthood, on through old age. Spock is featured in more segments of Star Trek than is Kirk.
3. Over the entire corpus of filmed adventures, Spock changes more than any other character, which is what we expect to happen to the main character.
What other evidence is there to support the idea that Spock is the main character of TOS?