Leonard Nimoy (center) with most of the Star Trek cast and NASA administrator James Fletcher (far left) at the 1976 unveiling of the Space Shuttle Enterprise. (Credit: NASA) The death of Leonard Nimoy yesterday inspired an outpouring of moving testimonials about his vast impact: as an actor, as a supporter of science and smart science fiction, as a voice of reason in media both traditional and digital. You can find these memorials all over Twitter, often accompanied by incredible photos, such as this on-set candid moment and a look at his sensitive moment as an advice columnist. Look at #LLAP (live long and prosper) and see what I mean. Even President Obama weighed in with an appreciation of Nimoy. Nimoy's indelible, decades-long performance as Mr. Spock is one of the greatest performances ever in science fiction. He was, in many ways, the central axis of Star Trek, and Trek's inspiring influence on three generations of young researchers is widely acknowledged. Spock's great importance as a role model of rational thought is also undeniable; in his tribute, Obama praised the character as "cool, logical, big-eared and level-headed." Spock's catch phrase was "fascinating." No wonder that Nimoy was so beloved by so many scientists. But the most interesting aspect of Spock is that he was not just a logical Vulcan. He was half-human, and the war between his ostensibly "rational" and "emotional" sides provided some remarkably subtle and insightful commentary on how science really works. Psychological duality is a staple of science fiction and fantasy. It defines every superhero who lives a civilian life but also dons a costume to act out his or her superpowers. It is the essence of characters ranging from the Incredible Hulk (id and ego, split in two!) to Harry Potter (the Muggle turned wizard). Spock follows in that tradition, and yet is truly unique. Neither the human nor the Vulcan side was his "true" personality. The struggle between the two sides was typically portrayed as his Vulcan side trying to suppress his base human impulses, and yet in the Star Trek universe--and especially in Nimoy's portrayal--it was clear that both sides needed each other equally. Put in pop-psychology terms, Spock had both emotional intelligence and rational intelligence, and he relied on both to succeed.