As far as iconic sci-fi characters are concerned, the first officer Spock from Star Trek is one of the most popular ones. He first appeared on the screen in times when aliens were usually portrayed as hostile beings, ready to invade the Earth. But Spock was different. Not only did he serve on a ship mostly filled with humans, but he was also friends with them, especially with Enterprise's captain James T. Kirk.
Spock was also unique in another area - he didn't show his emotions. He was intelligent, sympathetic, and had a subtle sense of humor. And even though multiple actors portrayed him, there can only be one true Spock.
Every story has to start somewhere, and Spock's story started with Leonard Nimoy - a whole decade before Zachary Quinto was even born. Nimoy was the only actor who reprised his role from the unaired Star Trek pilot The Cage. He stuck with the series for its entire run, reprised his role in the six feature films and in Star Trek: The Next Generation as well. Plus, it was the popularity of his character that helped make Star Trek the phenomenon it is today.
The fact is that before J.J. Abrams and the new cast kickstarted Star Trek back in 2009, many younger people had no idea there was the original Star Trek series. The film trilogy, in many ways, brought Star Trek back to the public eye and once again reminded everyone what a huge universe it was. Zachary Quinto's Spock was an important part of that since he was one of the main characters of the first, as well as the subsequent movies.
A lot of the gestures and characteristics typical for Spock come from Leonard Nimoy. He was the one who devised the Vulcan salute - "Live long and prosper." Zachary Quinto, as well as other actors playing Vulcans, continue using the salute to this day! Another trait that Nimoy provided was Spock's characteristic eyebrow raise or the Vulcan nerve pinch he uses to stop his enemies without the need to resort to unnecessary violence.
Leonard Nimoy's Spock was also in touch with his emotions - but Zachary Quinto's Spock is a more human Spock. Partially because the first film also puts emphasis on his relationship with his parents - a Vulcan father and a human mother.
Spock is somewhat conflicted about being half-Vulcan, half-human, especially once his mother dies, and this is something Leonard Nimoy didn't have the opportunity to explore as much as Zachary Quinto did.
With a few notable exceptions that were mostly caused by unusual circumstances, Leonard Nimoy's Spock didn't really have romances in the series. And that fits well with what the fans know about Vulcans since they're much more reserved at forming relationships, especially with non-Vulcans. That's the reason why Spock's existence in itself was somewhat controversial. On the other hand, the new Star Trek series paid a lot of attention to the budding romance between Spock and Uhura, and many fans felt this was one of its weaker points.
In one of the most fascinating scenes of the 2009 film, the younger version and older version of Spock meet. Leonard Nimoy reprised his role in the movies, and Nimoy's Spock had a brief conversation with Zachary Quinto's Spock. As for what Nimoy thought about Quinto's performance, he approved of the casting and expressed his support for Quinto. The two actors became friends in the end.
Technically, two people were the ones most responsible for the creation of the Kelvin timeline - the Romulan commander Nero (played by Eric Bana), and Leonard Nimoy's Spock.
When Spock failed to stop Romulus from being destroyed, he ended up traveling in time as well as Nero which created the alternate timeline. In other words - if it wasn't for Nimoy's Spock and his actions, there would be no Zachary Quinto's Spock.
It's a small detail but a significant one nonetheless. Not only was Leonard Nimoy's Spock highly intelligent and an excellent first office/science officer, but he also had a great singing voice. As a result, one of the most memorable scenes of the show came to be - forced to do so by hostile aliens, Nimoy's Spock sings the song Maiden Wine to Uhura and Christine Chapel. What makes this scene even more impressive is the fact Leonard Nimoy wrote the song himself!
The undeniable fact is that Zachary Quinto's Spock offered a new portrayal of Spock - one that had shared many traits with his predecessors but was also different in significant ways. Quinto's Spock is closer to his parents. He's more emotional, most likely because of his planet's destruction and his mother's death. And there's also the already-mentioned romantic relationship with Uhura, as well as other details - such as Spock's job at the Starfleet Academy that wasn't present during Leonard Nimoy's run as Spock.
One of the greatest things about the original Star Trek series was the iconic friendship between Captain Kirk and Spock. The show wouldn't work just with Spock or just with Kirk, not as well as it did with both of them. The new films tried to emulate the friendship between Kirk and Spock but it didn't have that much space to show how the bond between the two men evolved, so, at times, it fell a little flat. And the fact that for a significant part of their lives were Leonard Nimoy and William Shatner friendly in real life as well also helped them to create a truly iconic duo.
