Star Trek's first failed pilot, "The Cage," where he played a more emotional version of Spock alongside Jeffrey Hunter's originally take on Captain Christopher Pike. Hunter declined to return for the second pilot, "Where No Man Has Gone Before," replaced by Captain James T. Kirk (William Shatner) which began one of the most enduring friendships in all of science fiction.
Spock was immediately popular with audiences, his cool, emotionless remove contrasting powerfully with the charismatic, swashbuckling Captain Kirk. The half-human, half-Vulcan officer was a child of two worlds, but found that he didn't really belong on either Earth or Vulcan. He found his home on the bridge of the USS Enterprise, exploring space with his close friends Kirk and Doctor Leonard "Bones" McCoy (DeForest Kelley) over three seasons on TOS. Spock became a cultural icon, starring in some of the most memorable and influential stories in the history of American television.
10 The Doomsday Machine
The USS Enterprise finds itself confronted by a weapon of unimaginable power, able to destroy entire worlds with little effort. With Kirk trapped on the heavily damaged USS Constitution, Spock is forced to manage command of the ship with the Constitution's commanding officer, Commodore Matthew Decker (William Windom), who is still clearly traumatized by the loss of his crew and the damage done to his ship by the planet killer weapon. Spock is forced to toe the line of Starfleet's chain of command while simultaneously preventing the destruction of the Enterprise through Decker's unwise tactical maneuverings.
9 The Naked Time
The USS Enterprise crew becomes infected with a virus that strips away inhibitions after surveying the remains of a doomed research laboratory above the planet Psi 2000. This results in some amusing, if dangerous, shenanigans among the crew, perhaps most famously a delirious, shirtless Hikaru Sulu (George Takei) menacing the crew with a fencing foil. The infection is perhaps hardest on Spock, whose emotional control comes crumbling down. Nimoy's portrayal of a desperate Spock attempting to gain control over his compromised emotional state was an early indication that Spock was a multifaceted, compelling character.
8 The Enterprise Incident
One of the few Star Trek: The Original Series season 3 episodes that still holds up despite that season's tumultuous production process, "The Enterprise Incident" sees Spock face off with a female Romulan Commander (Joanne Linville) as he and Kirk follow covert orders to attempt to acquire a Romulan cloaking device. Spock and the Romulan Commander have immediate chemistry, with Spock assuming the role of seducer that Kirk often filled during TOS. They succeed in their mission, but Spock comes away with mixed feelings when the Romulan Commander is ultimately captured, feeling he and the Romulan could have had something under different circumstances.
7 Balance Of Terror
"Balance Of Terror" is often hailed as one of the best episodes of Star Trek: The Original Series, and served as the template for the alternate future glimpsed in Romulans physically resemble Vulcans, Spock conveys his shock with a trademark raised eyebrow. Spock must deal with some nascent bigotry from some of his fellow officers as the USS Enterprise attempts to navigate a situation that not only could cost them their lives, but potentially start a war.
6 The Menagerie
Conceived as a clever cost-cutting use of footage from "The Cage," the original unused Star Trek: The Original Series pilot, "The Menagerie" stands as an unintentionally important moment in the overall Star Trek mythos. After Captain Christopher Pike (Sean Kenney) is critically injured in a training accident, Spock commandeers the USS Enterprise and sets a course for Talos IV, a forbidden planet he and Pike visited years earlier. Spock hopes the powerful Talosians can grant Pike a comfortable, illusory life after his injury. Spock puts his career and life on the line to help his former Captain one last time.
5 Mirror, Mirror
A transporter accident sends Kirk, McCoy, Montgomery "Scotty" Scott (James Doohan), and Nyota Uhura (Nichelle Nichols) to the Mirror Universe, a dark alternate reality where the United Federation of Planets is replaced by the evil Terran Empire. Kirk and friends are forced to navigate a ship full of killers and crooks as they attempt to get home. The most affecting member of the Mirror Universe is Spock, recast as a duplicitous henchman with hopes of overthrowing his Captain Kirk and ruling the Terran Empire himself. It's a dynamic, terrifying performance from Nimoy, proving he had a bit more acting range than many may have believed at the time.
4 The Galileo Seven
A scientific expedition gone wrong forces Spock - in command of an away team aboard the shuttle Galileo - to land his shuttle on the planet Taurus II. Spock's leadership is called into question by his fellow shipmates when it becomes clear the shuttle can't relaunch with the full crew aboard, and the native anthropoids begin killing the away team . With Scotty's shuttle repairs moving slowly and his team being hunted, Spock is forced to make some difficult command decisions and earn the trust of the fraying away team. It's the first time Spock proves not only his inherent intelligence, but his ability to lead others in a crisis.
3 The Devil In The Dark
The USS Enterprise is dispatched to Janus VI, a mining planet where the miners and their equipment are being accosted by a mysterious creature. After the creature kills several miners, Kirk and Spock track it down. The creature is revealed to be a Horta, a hideous mass of rock and plasma. Spock attempts to communicate with the creature via a Vulcan mind meld, where it's revealed the Horta is not malicious, but is simply injured and protecting its offspring, which was unintentionally ravaged by the miners. The mind meld scene is one of Nimoy's best performances, expertly channeling all the grief and pain the Horta is experiencing.
2 Journey To Babel
"Journey To Babel" is a strong episode of Star Trek: The Original Series on its own merits, featuring a murder conspiracy and a cavalcade of charmingly dated alien species. But the episode is monumental because it features the first onscreen meeting between Star Trek: The Next Generation, but "Journey To Babel" is the story that established the basics of what is arguably Star Trek's most important father and son story.
1 Amok Time
One of the most famous episodes of Star Trek: The Original Series sees Spock suffering from pon farr, the biological phenomenon that compels male Vulcans to mate every seven years. After diverting the USS Enterprise to Vulcan so that Spock can be united with his betrothed T'Pring (Arlene Martel), Captain Kirk is forced into ritual combat with his Vulcan First Officer. Kirk's death is faked with a timely assist from Dr. McCoy, and Spock's elation at the realization he did not kill his friend stands as one of the most emotionally satisfying moments in all of Star Trek: The Original Series.