Spock/Relationships/Friendships/James T. Kirk

Spock first met Kirk aboard the Enterprise in 2259, when it was under command of Fleet Captain Christopher Pike. ()
In 2265, after the death of Gary Mitchell, Spock's detached and logical analysis was relied on by Kirk as a supplement to his own intuitive and impulsive nature. Their official relationship deepened into a friendship of mutual respect and love that was, without a doubt, the most important relationship of both Spock and Kirk's life. As Edith Keeler observed of Spock's place in the world, "You? At his side. As if you've always been there and always will." () 
Kirk once described his Vulcan friend as "the noblest half of myself" and declared that Spock's immortal soul "is my responsibility, as surely as if it were my very own." Kirk even told Spock's father that he would never realize how important Spock was to him, and declared that, despite losing the Enterprise and his son, had he not tried to rescue his friend, "the cost would have been my soul." ()
The polywater intoxication that affected the Enterprise crew in 2266 led to a difficult encounter between Spock and Kirk. When Spock was urgently required by his commanding officer, an anguished and reflective Spock was found by Kirk, Spock regretting his inability to express love even for his mother. Trying to bring the first officer around to the moment, Kirk slapped him. Spock's reaction was flat and revelatory, "Jim, when I feel friendship for you, I'm ashamed." Struck again, Spock responded in kind, sending Kirk backwards over a table. ()
Spock was sympathetic to Kirk's plight after the transporter divided the captain's personality into opposite aspects. He referred to his own halves, "submerged… constantly at war with each other." Spock believed that Kirk could survive such a contest intact, and urged him to embrace the part of himself that, seemingly ugly, was crucial to his personality and captaincy. ()
After Kirk discovered emotional rage was the key to nullifying the effect of the pod plants' spores, his first step in retrieving his crew was to taunt Spock into anger. Anticipating the result of a Vulcan's strength pitted against him, Kirk wielded a pipe for protection. After calling him an "elf with a hyperactive thyroid" and saying he belonged "in the circus, right next to the dog-faced boy," Spock indeed lost control, nearly killing Kirk before regaining control of himself. ()
In 2267, Spock began his pon farr mating cycle, and behaved bizarrely aboard the Enterprise. Kirk called Spock "the best first officer in the Fleet" and "an enormous asset to me" as he pled with Spock to explain his actions. When told that taking Spock to Vulcan was against Starfleet orders, Kirk fired back, "I owe him my life a dozen times over! Isn't that worth a career?" Joining him on Vulcan for his marriage ceremony, Kirk was drawn into T'Pring's scheme to marry another, and forced to fight Spock to the death. McCoy, knowing Kirk was endangered, faked Kirk's death, and the marriage was not consummated. Spock, despondent that he had murdered his captain, was thrilled at the sight of Kirk alive, exclaiming, "JIM!" which McCoy delighted in needling Spock about, once he gained his composure. ()
Kirk's understanding of Spock had an enormous impact on the parallel mirror universe, visited after a transporter accident in 2267. As Kirk's party prepared to return to their proper universe, Kirk implored the to re-examine his role in the fascistic Terran Empire, insisting, "One man can make a difference." Mirror Spock's consideration of those words led to his rise to dominance and reform of the Empire, with drastic consequences. (; )
When Kirk was trapped in spatial interphase during a rescue operation in Tholian space, Spock ordered the Enterprise to maintain its position in an effort to retrieve him, in spite of the danger the Tholians presented and the disruptive nature of the local space. After Kirk's assumed death, Spock and McCoy viewed the "last orders" Kirk had prepared. He urged Spock to use all the Vulcan disciplines at his disposal, tempered with intuitive insight. Kirk believed Spock had the latter qualities, but should they elude him, he was urged to seek out McCoy. ()
Kirk once commented to Captain Garth that he and Spock were "brothers". Spock merely responded, "Captain Kirk speaks somewhat figuratively, and with undue emotion, but what he says is logical and I do, in fact, agree with it." ()
When Dr. Janice Lester, a former lover of Kirk's, took over Kirk's body, Spock performed a mind meld on Kirk while he was trapped in Lester's body. Spock believed Kirk was Lester before anyone else, and when Lester as Kirk ordered his execution, he continued to stand by his friend. ()
At the end of the Enterprises five-year mission, a period marked by his frequent loss of emotional control, Spock chose to leave Starfleet and his friends, to pursue the kolinahr discipline of logic on Vulcan. His return to the Enterprise during the V'ger threat was a cold event, without acknowledgment of his past friendships. In V'gers aftermath, Spock finally achieved equilibrium, able to express his friendship for Kirk without the influence of aliens or illness, and notably lacking any threat of physical violence. In 2285, Spock was calmly able to tell Kirk, "You're my superior officer. You are also my friend. I have been and always shall be yours." (; )
Spock's sacrifice of his own life, to save the Enterprise from Khan's detonation of the Genesis Device, deeply affected Kirk. At his funeral, Kirk could only bring himself to say of Spock, "Of all the souls I have encountered in my travels, his was the most… Human." ()
The revelation that Spock's katra, his living spirit, survived in the tormented mind of McCoy, led Kirk to risk his career, and in turn, his crew's. He first asked Fleet Admiral Morrow for permission to retrieve Spock's body from the Genesis Planet, to bring it, and McCoy, to Vulcan. Kirk insisted that any chance to save Spock's soul was his responsibility, "as surely as if it were my very own." His request declined, he told his crew, "the word is No. I am therefore going anyway." 
With the help of Uhura, Scott, Sulu, and Chekov, Kirk rescued McCoy from confinement and commandeered the Enterprise from Spacedock One. The renegade mission saw the death of Kirk's ship as well as his son. Finding Spock's body re-animated by Genesis, Kirk brought him and McCoy, to Vulcan for the fal-tor-pan (re-fusion) ritual. The first person Spock recognized was Kirk: "Jim. Your name, is Jim." ()
During their homecoming from Vulcan, and eventually their trip to 1986, Kirk tried to remind the resurrected Spock, suffering from memory loss, of their friendship and past adventures together. After Kirk and the crew's trial, Spock told his father, his "associates" were his friends. ()
In 2287, Spock accompanied Kirk and McCoy on a camping trip together at Yosemite National Park, which abruptly ended when Spock's half-brother, Sybok, diverted the Enterprise to Nimbus III. After their adventure on and Sybok's death, Kirk referred to Spock once again as his "brother", and told him and McCoy that they were his real family. ()
When Spock later entered the alternate reality, he told of their deep friendship, despite the fact that had marooned Kirk on . Before returning Kirk, along with , to the (revealing to this Scott an advancement in transporter technology over a century before his prime counterpart perfected it), Spock – who in this reality had designed the Kobayashi Maru simulation and openly begrudged Kirk outsmarting it – was reminded that this could be viewed as "cheating", to which he replied that an "old friend" – namely, Kirk – had taught him how to cheat.
Later, when Spock Prime spoke to his own alternate reality counterpart about that universe's Kirk, he explained that he had resorted to a level of subterfuge in order to inform both men of the necessity of their friendship, both to themselves and to others. Spock Prime explained, "I could not deprive you of the revelation of all that you could accomplish together, of a friendship that will define you both in ways you cannot yet realize." ()