Spock
Now: Zachary Quinto
He's turned in work on CSI and 24, but the furry-browed actor is best known for his role as skull-splitting, shape-shffting serial killer Sylar on Heroes.
Then: Leonard Nimoy
Since his days on the Enterprise ended, Nimoy has popped up doing voice-over work on projects such as A&E's Ancient Mysteries and appearances on Futurama and The Simpsons. He most recently appeared in Star Trek director J.J. Abrams' Fox series Fringe as William Bell, the mysterious former partner of Walter Bishop. He will also reprise his role as Spock in the Trek reboot.
