Leonard Nimoy didn't just have a massive impact on science fiction, he also transformed pop culture. Nimoy, who died today, took the thankless supporting role of an emotionless alien science whiz, and turned Spock on Star Trek into an icon.
Before Spock came along, alien beings in mass media (and most written SF as well) were one-dimensional. They represented the "other," the strange and unknowable beings who could only throw our human characters in relief. In the hands of most actors, Spock would have been a one-note joke character: the guy who spouts off formulas and equations in a monotone. Spock could easily have become the butt of Star Trek's jokes, or just a weird side character.
But Nimoy imbued Spock with a life and complexity that were impossible to deny. Far from being a one-note character, Spock became one of the most complex and nuanced people on television. From his inner torment to his quiet amusement at the humans around him to his occasional flashes of anger, Spock was a constantly surprising mystery, with a lot of layers.
As I wrote a few years ago (in a piece that I was overjoyed that Nimoy retweeted):