The time I met him, it was his sense of humor that stood out.
After the first Apollo lunar landing, I was a graduate student in Applied Space Science at Carnegie Mellon University. Clarke had come to campus to talk about the future of space exploration, as embodied in his then-recently-published book "The Promise of Space."
After the presentation, a group of us hung around to have a chat with a person we regarded as an icon of space exploration in addition to a science fiction master. But before I left for the lecture, I looked for anything to take that he could autograph in case the opportunity aroseso I grabbed a photo of Apollo astronaut Buzz Aldrin saluting the U.S. flag on the moon. When I was able to present it to Clarke to sign, he modestly said, "I had nothing to do with this!"
The conversation later turned to prospects for teleportation, as with the then-recent TV series Star Trek's transporter. I asked might such devices make rocket-based space technology obsolete for conveying people. Because the world at that time was not as "digital" as it is today, Clarke said it might eventually be possible, but we would have to ensure no "60-cycle hum" would be superimposed on people being transported, lest they emerge with a sine-wave texture!
As he was leaving, he noted he was off to New York to join "Wally, Walt, and Don" (astronaut Wally Schirra, newscaster Walter Cronkite, and astronaut Don Eisle) for television coverage of the next Apollo missionwhich turned out to be the near-disastrous Apollo 13.