These six Captain James T. Kirk (William Shatner) and Commander Spock (Leonard Nimoy). Kirk and Spock are the most iconic duo in Star Trek; ed by Dr. Leonard "Bones" McCoy (DeForest Kelley), they become the signature trio of the Star Trek franchise. Kirk and Spock have been through death and life together in their decades of voyages aboard the USS Enterprise.

It's easy to take for granted that Captain Kirk and Mr. Spock were always bosom buddies. Star Trek: Strange New Worlds season 2 depicted Lieutenant Kirk (Paul Wesley) meeting Lieutenant Spock (Ethan Peck) when they were introduced by Ensign Nyota Uhura (Celia Rose Gooding). Although Star Trek: The Original Series established the Starship Enterprise's paradigm of Kirk as the dynamic leader and Spock as his loyal second-in-command, the Captain and the Vulcan Science Officer took time to develop their unbreakable bond.

Most of the iconic and heartwarming moments of friendship and brotherhood between Captain Kirk and Spock happened after Star Trek: The Original Series season 1. From Spock's joy at finding Kirk alive at the end of movies, the seeds for Kirk and Spock's eternal friendship were more subtly planted in Star Trek's inaugural season.

6 "The Enemy Within"

Star Trek: The Original Series Season 1, Episode 5

When Captain James T. Kirk is split into 'good' and 'evil' halves by a transporter accident, certain death looms for the Captain of the Enterprise as his two sides can't live without the other. Spock is by Kirk's side as the USS Enterprise's leaders slowly realize that there's a malevolent version of the Captain aboard. Without Spock's , the two Kirks couldn't have been merged back to normal.

"The Enemy Within" is an early example of Spock's loyalty to Captain Kirk. While Spock was acting in his role as First Officer, the Vulcan was also watching Jim's back out of friendship and genuine concern that the Captain would die if he wasn't reunited with his 'evil' half. Spock also used the Vulcan nerve pinch for the first time as a non-violent way to subdue the evil Kirk.

5 "The Menagerie Parts 1 & 2"

Star Trek: The Original Series Season 1, Episode 11 & 12

Talosians to bring the critically injured Fleet Captain Christopher Pike (Sean Kinney) to Talos IV. Spock was court-martialed by Captain Kirk and Commodore Jose Mendez (Malalchi Throne), but once the truth about Spock's actions was revealed, Pike was allowed to live out the remainder of his life on Talos IV.

Star Trek: Strange New Worlds revealed that Captain Pike (Anson Mount) told Lieutenant Spock about his destiny to be horribly disfigured by delta rays years before it happened.

"The Menagerie" is based upon the loyalty Spock has for Pike, his former Captain aboard the USS Enterprise, but Captain Kirk's actions towards Spock are notable. Kirk wanted to believe Spock was innocent of mutiny, and he silently ed his Vulcan friend as they all learned the truth about Captain Pike's (Jeffrey Hunter) previous arrival on Talos IV. "The Menagerie" showed that Kirk reciprocates the loyalty Spock always shows him.

4 "The Conscience of the King"

Star Trek: The Original Series Season 1, Episode 13

Captain Kirk becomes obsessed with determining whether a Shakespearean actor performing aboard the USS Enterprise, Anton Karidian (Arnold Moss), is Kodos the Executioner, who killed thousands of people when Kirk was a boy. Kirk also becomes infatuated with Karidian's young daughter, Lenore (Barbara Anderson), who turns out to be a serial killer protecting her father's dark secret. In the end, Lenore's insanity goes over the edge when she accidentally kills her father with a phaser.

Spock shows genuine concern for Captain Kirk after monitoring Jim's behavior towards the Karidians. Although Dr. Leonard McCoy was dismissive of Spock's unease, the Vulcan Science Officer did the necessary research to uncover Kirk's past connection to Anton Karidan's alter ego. Spock is the voice of reason, pulling Kirk back from the brink in Star Trek: The Original Series, "The Conscience of the King," and the Vulcan helped Kirk survive Lenore's assassination attempt on his Captain.

3 "Space Seed"

Star Trek: The Original Series Season 1, Episode 22

The Starship Enterprise intercepts a 20th-century Earth vessel, the SS Botany Bay, which contains the cryogenically frozen Khan Noonien Singh (Ricardo Montalban) and his genetically engineered followers. The revived Khan attempts a hostile takeover of the Enterprise and tries to kill Captain Kirk. However, with Spock's help, Kirk defeats Khan and regains control of the Enterprise before banishing Khan and his minions to the planet Ceti Alpha V.

The Captain of the Enterprise allowed his First Officer to aggressively question Khan while Kirk searched for weaknesses.

During a tense dinner, Khan quickly understood one of the vital functions Spock serves for Kirk: The Captain of the Enterprise allowed his First Officer to aggressively question Khan while Kirk searched for weaknesses. When Khan seized control of the starship and placed Kirk in a death trap, Spock helped turn the tables on Khan's enforcers so that the Captain could confront and subdue Khan. Spock's intellect and abilities were a match for Khan's, and Kirk couldn't have survived this crisis without his Vulcan friend.

2 "Errand Of Mercy"

Star Trek: The Original Series Season 1, Episode 26

Captain Kirk and Mr. Spock beam down to the planet Organia to warn the natives of the imminent arrival of the Klingons. While Kirk and Spock are trapped on the planet, the Organians behave in a puzzlingly ive manner that frustrates the Starfleet Officers and Klingon Commander Kor (John Colicos). The Organians eventually reveal themselves to be powerful non-corporeal beings who prevented war between the Klingons and Starfleet.

"Errand of Mercy" was one of the most notable landing party team-ups between Captain Kirk and Spock in Star Trek: The Original Series season 1. Spock survived the Klingons' deadly mind-scanner weapon thanks to his Vulcan mental discipline, and he and Kirk worked together to sabotage the Klingons' occupation of Organia. Spock and Kirk display what a formidable and effective team they are, setting the stage for more adventures and victories the duo will share.

1 "The City on the Edge of Forever"

Star Trek: The Original Series Season 1, Episode 28

Perhaps the most notable and iconic two-hander by Captain Kirk and Spock in Star Trek: The Original Series season 1 is "The City on the Edge of Forever." Considered Star Trek's greatest episode, Kirk and Spock time-travel to New York City in 1930 to stop Dr. Leonard McCoy, who was driven mad by an accidental drug injection, from altering history. Kirk and Spock also learn that Sister Edith Keeler (Joan Collins) is a focal point whose death is crucial to ensure history unfolds as it should.

Edith Keeler astutely summed up Spock when she said his place is by Captain Kirk's side as if he always was and always will be. Indeed, Spock was burdened with two huge responsibilities. Spock had to repair his Tricorder to learn about Keeler's pivotal role in history, and the Vulcan Science Officer showed concern and comion for Captain Kirk, who'd fallen in love with Edith Keeler. When Kirk did what history demanded and let Edith die, Spock fully understood how his Captain sacrificed his needs for the needs of the many in Star Trek: The Original Series season 1.