Question: Just who was Number 1?
Chosen answer: We were never told. In the series finale [Spoiler alert] Number 6 demands an answer to that question, only to be shown his own reflection.
Answer: The Prisoner was first shown on British television in 1967. I did not watch it then, but the series was was repeated on UK television in 1977, at which point it became a massive cult. Certainly, I was hooked. Well, ten minutes after I started watching The Prisoner, I was 110% certain as to who Number 1 was. In my opinion, the identity of Number 1 was so utterly, glaringly obvious that I could not understand how anybody could even ask such a question. I thought there was only one candidate for the identity of Number 1, and it was so plainly visible that nobody could even vaguely consider it to be anybody else. So, who did I think Number 1 was? you all ask. My answer? Himself! Patrick McGoohan (or rather, the character Patrick McGoohan played in The Prisoner) was Number 1. I was proved right. In Fall Out, the seventeenth and final episode, "The Prisoner" gets to meet "Number 1." Now this is a real "blink and you'll miss it" moment, but Number 1 has his face covered. The Prisoner pulls off the covering to see a mask, he pulls off the mask, to see himself! The Patrick McGoohan in Number 1's costume laughs in The Prisoner's face and runs away. Unfortunately, I don't know why Patrick McGoohan should be both The Prisoner and Number 1. I don't think anybody does.
Question: Why was this series cancelled after three seasons?
Answer: It's even more obvious than you think, you know who number 1 is in the very first episode. When 2 replies to the question "who is #1?" Change the way he answers from you are number one (in the monotone or accented answer to, "You are, number 6. The comma gives you the answer. #6 is #1. It's the tone of the answer.