There are three shows I remember from being a small child: the 60s Spider-man cartoon, the Adam West Batman and Star Trek. Those were the first shows I have strong memories of, and of those three, Star Trek was the show I watched the most growing up. It was always on TV (Channel 4) though occasionally it would get replaced by some other program, like Big Valley, which I still haven't quite forgiven for that bit of chicanery. We played Star Trek at recess in school, and we took turns on being the various characters from the show. Of course, the big three were always in demand, and Mr Spock was always the coolest person to play.
At that age, one didn't realize the quality of acting going on, we just enjoyed the show. Leonard was great as Spock, even in some of the episodes that are not quite as good as they should be. "Spock's Brain", I'm looking in your direction! Even then he never lowered his performance.
As I got older, it was fun seeing him in other, older shows and movies; he appeared in one of the Rocketman serials, an episode of Outer Limits, and then was in Get Smart. Following ST, he did a memorable stint in Mission: Impossible.
He was always there in my life. I don't remember any time he wasn't there. I'm going to miss him.