Throughout the history of the universe, there have been multiple timelines, alternate realities and parallel universes that have all contained versions of James T. Kirk, as well as various clones and replicants.
James T. Kirks
Other versions of James T. Kirk
In an alternate timeline in which John Frederick Paxton destroyed Starfleet Command and ended the talks for the Coalition of Planets in 2155, James T. Kirk became resentful of aliens in general and Vulcans in particular when the Interstellar Coalition starship ICV Vanik destroyed a transport carrying his wife and son. By then, he was serving as first officer aboard UESS Enterprise under Captain Christopher Pike. Six months later, in 2264, had to face his prejudices when the Enterprise carried Lady T'Pol to Babel to negotiate United Earth's admission to the Interstellar Coalition. (ST - Myriad Universes novel: A Less Perfect Union)
In another alternate timeline in which the Vulcans had remained a violent and emotional species, James T. Kirk commanded the IUES Enterprise I, a Charter-class starship of the Interstellar Guard in service in the 2260s. Many of his crewmates went on to have successful careers in the Guard, including his first officer, Gav, who became a Brigadier General in the Security Bureau, tactical officer Lamia, who became a Major General on Field Marshal Thelianaresth th'Vorothishria's staff, and astrophysicist Hikaru Sulu, who served as Captain of the IUES Kumari II, the flagship of the IG Fleet. (ST - Myriad Universes novel: The Tears of Eridanus)
In an alternate timeline created when Yeoman J. Mia Colt was sent forward in time from 2254 to 2293 after her tricorder scans released the tachyon energy contained in an Algolian artifact known as a Keepsake, Kirk, who had recently graduated from Starfleet Academy, was assigned as Captain Christopher Pike's yeoman. Due in part to Pike's grief at Colt's disappearance as well as their divergent personalities, Pike and Kirk had an extremely contentious relationship. No longer able to stand being in Pike's presence, Kirk resigned his Starfleet commission and entered the commercial sector. He eventually became the commanding officer of the freighter Bounty. Pike remained in command of the Enterprise until it was decommissioned, after which it became a popular attraction at the San Francisco Smithsonian Museum of Air, Sea and Space. He was then placed in command of the USS Enterprise-A.
Following Colt's reappearance in the Enterprise exhibit in San Francisco in 2293, she made contact with Kirk and arranged transport on the Bounty to Algol II, which had been conquered by the Klingons in 2278. When the Bounty came under attack from a Klingon bird-of-prey commanded by General Chang, the Enterprise-A arrived on the scene and defeated the Klingon vessel, though immediately took the Bounty crew into custody. After discovering that Colt, who had not aged a day since her disappearance, was aboard the Bounty, Pike eventually agreed to go along with Kirk's plan and return Colt to her own time through the Well of Tomorrows on Algol II. The USS Excelsior, under the command of his former first officer Number One, was dispatched by Starfleet Command to prevent the Enterprise from entering the Klingon Neutral Zone. However, when she made contact with Pike, she allowed him to proceed to the planet. The Enterprise soon came under attack from Chang's bird-of-prey and three Klingon battle cruisers. The ship was severely damaged in the battle, during which Sulu and Saavik were killed. In order to prevent the surviving crew from being captured by the Klingons, Pike activated the self-destruct sequence. As the Enterprise was destroyed, Colt entered the Well of Tomorrows and was returned to 2254, thereby restoring the proper timeline. (EV comics: "Future Tense", "Futures", "Now and Then")
The Chimes at Midnight
In another alternate timeline created by the death of Spock in 2237, the half-Andorian / half-Aenar thaan Thelin th'Valrass served as Kirk's first officer aboard the Enterprise from 2265 to 2270. Thelin developed a close friendship with Kirk and, along with Dr. Leonard McCoy, served as one of the captain's key advisors over the course of their five-year mission. The more logical McCoy served to temper Thelin's impulsive, emotional nature.
By 2285, Kirk was an instructor at Starfleet Academy and was responsible for reviewing the performance of cadets in the Kobayashi Maru Test aboard the Enterprise, which was by then under Thelin's command. While on a training voyage in March of that year, Kirk encountered Khan Noonien Singh for the second time and, with Thelin's consent, resumed command of the Enterprise. Although they were eventually able to defeat Khan, the Augment activated the Genesis Device with his dying breath while in the Mutara Nebula in the hope of destroying the Enterprise and thus gaining his revenge against Kirk. However, Thelin and Kirk's son David Marcus were able to configure the Enterprise's shield to allow the ship and its crew to survive the effects of the Genesis Wave. Nevertheless, several cadets were genetically mutated as a result of their exposure to the wave.
Only days later, while investigating the newly formed Genesis Planet, David and Saavik were captured by Commander Kruge of the Klingon bird-of-prey IKS Katai. Two months after that, Kruge contacted the disgraced former spy Arne Darvin and paid him to inform Thelin that David and Saavik were still alive and that Kruge was willing to release them in exchange for all Federation data concerning Genesis and an operational Genesis torpedo. Shortly afterwards, Kirk and his former crew stole the Enterprise from Spacedock and rendezvoused with the Katai. While Kirk appeared to accede to Kruge's demands, the Enterprise transported Pavel Chekov aboard the Katai in a mock Genesis torpedo. Chekov proceeded to beam Kirk, Thelin and Hikaru Sulu aboard the Katai and they promptly gained control of the ship and rescued the hostages.
The captured Klingons briefly gained the upper hand when Maltz accessed the Katai's weapon console and fired at the already damaged Enterprise's warp core. Kirk attempted to bring the Enterprise's auxiliary power systems online and prevent a warp core breach. His efforts were unsuccessful. Reflecting that the Enterprise was part of his past and that he should instead look to the future and build a true relationship with David, he instructed Montgomery Scott to beam him aboard the Katai. However, given that the warp core breach had caused Engineering to be flooded with gamma radiation, Scotty was unable to lock onto him and he was killed in the destruction of the Enterprise. Immediately before his death, Kirk realised that he was finally facing a no-win scenario. In retribution for the death of his former commanding officer and close friend, Thelin vapourised Maltz. For years afterwards, David was wracked with guilt over his father's death, holding himself responsible. (TOS - Myriad Universes novella: The Chimes at Midnight)