John Connor sends Kyle Reese, one of his most trusted soldiers, back in time to 1984 to protect his mother Sarah whom Skynet has targeted for termination. A Terminator has also been sent back to kill Sarah, thereby preventing her from ever giving birth to John and ensuring Skynet's victory in the war. Reese not only protects Sarah but is also directly responsible for John's very existence as he and Sarah become involved and experience a night of passion together. It is during this romantic rendezvous that John is conceived, though Kyle does not survive to see John's birth as he is killed by the Terminator hours later.
Terminator 2: Judgment Day
Eleven years later, John (portrayed by Edward Furlong) is living with foster parents while his biological mother is incarcerated at Pescadero Psychiatric Hospital. Though a rebellious pre-teen, he is street-smart and has already been taught a great deal about warfare and survival by friends of his mother's to prepare him for his destined role as leader of the human resistance against Skynet. Though he is not entirely convinced by Sarah's tales of a nightmare future ruled by machines, the arrival of a Terminator sent back in time to protect him makes him realise the truth.
With the help of his cyborg defender, John rescues his mother from Pescadero and together they attempt to change the future by destroying Cyberdyne Systems, the company responsible for creating Skynet. Though they are relentlessly pursued by a T-1000 android and many innocents are caught in the crossfire, the Connors succeed in destroying all of Cyberdyne's research and the remains of the first Terminator that had tried to kill Sarah a decade previously. After both the T-800 and T-1000 are destroyed in a pit of molten steel, it seems that there is now hope for the future.
Terminator 3: Rise of the Machines
In 2004, John (portrayed by Nick Stahl) lives as a vagrant with no address, no phone and no means of being tracked down. Despite his previous efforts to prevent Judgment Day, he still does not believe that he is out of danger, and he is proven right when a T-X arrives on a mission to kill John and his future lieutenants in the Resistance. Once again, John finds himself being protected by a reprogrammed Terminator. This reprogrammed T-850 sent back by the Resistance to protect John and his future wife Kate Brewster reveals that John was killed in combat in the year 2032 and that it was the machine that carried out the termination. In 2004, John did not appreciate the irony of being protected by his own killer, but it was thanks to the Terminator that he and Kate made it to the Crystal Peak fallout shelter and survived Skynet's nuclear attack on humanity.
In the fifth Terminator film, the entire continuity of the franchise is radically altered. In 2029, on the eve of humanity's final battle against Skynet, John Connor (played by Jason Clarke) and his Resistance unit capture what appears to be a Skynet internment camp, but is actually a research complex containing Skynet's Temporal Displacement Device. A Terminator has already been sent through on a mission to 1984 to assassinate John's mother Sarah and so John sends Kyle Reese into the time displacement sphere to follow it and protect Sarah.
Whilst John and his comrades stand and watch as Kyle vanishes into the timestream, John is suddenly ambushed by one of his soldiers, Alex. As it turns out, Alex is actually a physical manifestation of Skynet's core consciousness; while the Resistance believed that Skynet's central core had been destroyed and its armies deactivated, the malicious AI had actually uploaded its consciousness into an advanced cybernetic body and infiltrated the Resistance. By touching John, Skynet infected him with nano-phase matter that reconstructed John on a molecular level, converting him into a T-3000. Now brought around to Skynet's way of thinking, John was sent back in time on a mission to ensure Skynet's dominance.
John traveled back to 2014 to aid Cyberdyne Systems with the Genisys Program to ensure the creation of Skynet, by providing the critical programming codes needed for the Genisys OS. He also used his position as the architect of Cyberdyne's new research campus to secure their funding for research into Time Displacement Equipment and mimetic polyalloy, which both reached the prototype stage by 2017, in turn hastening the development of Skynet's technologies.
In 2017, John met with his parents Kyle and Sarah shortly after their time-jump from 1984. Shortly after this meeting, his now-hybrid nature was exposed by Sarah's T-800 Guardian. John understood that Guardian's presence is what altered the timeline and wondered who sent him back in time. John tried to persuade Kyle and Sarah into joining him as a family, but they refused. John relentlessly pursued them and sped up the activation of Genisys.
John first tracked the Guardian and his parents down to Guardian's hideout as it was the place John's mother always told him about. After a fierce chase, the trio were arrested and taken to the police station. There, John impersonated a detective and infiltrated the building. The Guardian sensed the presence of John and saved Detective O'Brien before John could kill him.
After chasing down the trio in a helicopter, John engaged in a brutal clash with the Guardian in Cyberdyne Headquarters — in which John primarily maintains the upper hand. However, with the help of Sarah and Kyle, the Guardian took John into the electromagnetic field of the prototype time machine. As a result of Guardian's exposed inorganic material since his outer sheath was destroyed a while earlier, John was destroyed when the energy field collapsed, but not before he knocked the Guardian into a vat of liquid polymimetic alloy during the struggle.
Terminator: Dark Fate
This film ignores the continuity of T3, Salvation and Genisys, establishing itself as the true sequel to T2: Judgment Day.
By destroying Cyberdyne and the remains of the original T-800, as well as the sacrifice of his reprogrammed T-800 protector, John and Sarah succeeded in erasing Skynet from existence. On August 29th 1997, life continued on as normal. Judgment Day had been averted.
However, the Connors were not yet out of danger. When Skynet had sent back the T-800 and T-1000, it had sent numerous other Terminators back as well, all dispatched to different periods in time. One of these Terminators, another T-800, had been sent back to 1998, a year after Judgment Day was meant to have happened. It tracked down Sarah and John to a bar in Guatemala and immediately shot John on sight. After killing John, the Terminator simply dropped its weapon and walked away, leaving a distraught Sarah to cradle her son's lifeless body.