In The Terminator the characters of Kyle Reese and the Terminator are from a previous iteration of the timeline. Because Reese makes multiple references to John Connor, this means that in the past of his timeline John Connor was conceived, most likely in the same way as depicted in The Terminator, ergo another iteration of Kyle Reese from another timeline had been sent back to protect Sarah Connor.
The First Timeline
In this, the first ever timeline, because there was no previous timeline, no Terminator arrived via a chrono-sphere in 1984 to terminate Sarah Connor. As such Sarah J Connor possibly lived a full life. Although the details of her life in this timeline are unknown, because Kyle Reese would also not have arrived via a chrono-sphere in 1984 to protect her, she did not conceive John Connor and also had no knowledge of the Terminators, Judgment Day or Skynet.
Other uncertainties in this timeline are when Skynet (by this or another name) became self-aware, and when or even if Skynet may have instigated Judgment Day. What is certain is that without the Neural Network Processor of a series 800, Cyberdyne Systems model 101 "Terminator" Infiltrator Unit to reverse engineer, technological development in the field of Artificial Intelligence would have occurred at a natural technological rate, therefore Skynet would not have been developed until after 1997.
However, because John Connor existed in the timeline that yle Reese originated from we can deduce that another iteration of Kyle Reese had travelled back in time to conceive John Connor,
01:52am
A series 800, Cyberdyne Sytems model 101 "Terminator" Infiltrator Unit was sent back in time to May 12th, 1984, using Skynet's Time Displacement Equipment, with orders to terminate Sarah Connor. Shortly afterward, Kyle Reese followed the Terminator back in time to save Sarah J Connor from termination.
[Source - Terminator 2: Judgment Day, Revised Final Shooting Script]
Much of the events in the second timeline are echoed in the third timeline, the Cinematic Timeline, with the key difference being that in the second timeline no Terminators arrived in 1994 because they had not been sent back in time in the previous timeline. It is from the future of this timeline that the iterations of the Terminator and Kyle Reese depicted in The Terminator originate from.
01:52am
A series 800, Cyberdyne Systems model 101 "Terminator" Infiltrator Unit arrived via a chrono-sphere at Griffin Park Observatory, Los Angeles, California. Shortly afterward, Kyle Reese arrived via another chrono-sphere in an alleyway in Los Angeles, California.
[Source - The Terminator]
1984, May 13th
Sarah was taken to a nearby hospital, while Reese's remains went to the LAPD coroner. Inside the Cyberdyne Systems factory, two employees pocketed the Terminators damaged Neural Network Processor.
[Source - The Terminator, Terminator 2: Judgment Day]
Crossing the border into Mexico Sarah, 6 months pregnant, had her photograph taken shortly after recording an audiotape for her unborn son.
[Source - The Terminator]
1985, February 28th
John Connor was born.
[Source - Terminator 2: Judgment Day]
Although Kyle Reese is his father, this iteration of John Connor is that depicted by Michael Edwards in Terminator 2: Judgment Day. This John Connor never befriends the reprogrammed series 800 Terminator as it was never sent back in time to 1994.
Skynet, an Artificial Intelligence, tasked with controlling the US Military Defence Network, went online.
[Source - Terminator 2: Judgment Day]
The reprogrammed Terminator that will be sent back in time to 1994 (Terminator 2: Judgment Day) to protect John Connor as a child relates when en-route to Salceda Ranch that this is the date Skynet went online in the events of the timeline it came from.
1997, August 29th
02:14am
Skynet became self-aware and launched pre-emptive nuclear attacks against the worlds leading military powers, which combined with the inevitable retaliatory nuclear attacks resulted in the death of 3 billion human lives and blanketed most of the developed world in nuclear fallout - Judgment Day.
[Source - Terminator 2: Judgment Day]
2029
2029, July 11th
01:52am
A series 800, Cyberdyne Systems model 101 "Terminator" Infiltrator Unit was sent back in time to May 12th, 1984, using Skynet's Time Displacement Equipment, with orders to terminate Sarah Connor. Shortly afterward, Sergeant Kyle Reese (DN 38416) volunteered to follow the Terminator back in time to save Sarah J Connor from termination.
[Source - Terminator 2: Judgment Day, Revised Final Shooting Script]
2029
2029, July 11th01:52am
A series 800, Cyberdyne Sytems model 101 "Terminator" Infiltrator Unit was sent back in time to May 12th, 1984, using Skynet's Time Displacement Equipment, with orders to terminate Sarah Connor. Shortly afterward, Kyle Reese followed the Terminator back in time to save Sarah J Connor from termination.
[Source - Terminator 2: Judgment Day, Revised Final Shooting Script]
What is known is that Skynet was online and self-aware before July 11th, 2029, as this is when Skynet, using the Time Displacement Equipment (TDE) sent a series 800, Cyberdyne Sytems model 101 "Terminator" Infiltrator Unit back in time to May 12th, 1984 with orders to terminate Sarah Connor. While the TDE was still active we can estimate from the events in the The Terminator that Kyle Reese must have followed the Terminator back in time to 1984. This creates the second timeline.The Second Timeline
Much of the events in the second timeline are echoed in the third timeline, the Cinematic Timeline, with the key difference being that in the second timeline no Terminators arrived in 1994 because they had not been sent back in time in the previous timeline. It is from the future of this timeline that the iterations of the Terminator and Kyle Reese depicted in The Terminator originate from.
1984
1984, May 12th01:52am
A series 800, Cyberdyne Systems model 101 "Terminator" Infiltrator Unit arrived via a chrono-sphere at Griffin Park Observatory, Los Angeles, California. Shortly afterward, Kyle Reese arrived via another chrono-sphere in an alleyway in Los Angeles, California.
[Source - The Terminator]
1984, May 13th
The events following the Terminator and Kyle Reeses arrival echo those that will occur in The Terminator with two key differences - Reese will not have possessed a photograph of Sarah Connor, and with John Connor having never been born Reese had never met him and was therefore unable to inform Sarah of her sons destiny. As seen in The Terminator, Reese and Sarah would have conceived John before facing the Terminator in the Cyberdyne Systems factory, where Reese would have died. Sarah, squashing the Terminator in a hydraulic press, would have survived.1984, May 14th
Sarah was taken to a nearby hospital, while Reese's remains went to the LAPD coroner. Inside the Cyberdyne Systems factory, two employees pocketed the Terminators damaged Neural Network Processor.
[Source - The Terminator, Terminator 2: Judgment Day]
The remains of the Terminator would have been "officially" covered up before later being loaned to Cyberdyne Systems whose most promising engineer Miles Bennett Dyson was then tasked with reverse engineering the technology.1984, November 10th
Crossing the border into Mexico Sarah, 6 months pregnant, had her photograph taken shortly after recording an audiotape for her unborn son.
[Source - The Terminator]
1985
[Source - Terminator 2: Judgment Day]
Although Kyle Reese is his father, this iteration of John Connor is that depicted by Michael Edwards in Terminator 2: Judgment Day. This John Connor never befriends the reprogrammed series 800 Terminator as it was never sent back in time to 1994.
1997
1997, August 4th[Source - Terminator 2: Judgment Day]
The reprogrammed Terminator that will be sent back in time to 1994 (Terminator 2: Judgment Day) to protect John Connor as a child relates when en-route to Salceda Ranch that this is the date Skynet went online in the events of the timeline it came from.
1997, August 29th
02:14am
Skynet became self-aware and launched pre-emptive nuclear attacks against the worlds leading military powers, which combined with the inevitable retaliatory nuclear attacks resulted in the death of 3 billion human lives and blanketed most of the developed world in nuclear fallout - Judgment Day.
[Source - Terminator 2: Judgment Day]
The remains of the Terminator sent back in time to terminate Sarah Connor will have been used to influence Miles Bennett Dysons understanding of AI. As such, Skynet will have existed earlier than in the preceding timeline and therefore instigated Judgment Day on August 29th, 1997.
2021-2028
2021
Kyle Reese was assigned to the 132nd under Major Perry.
[Source - The Terminator]
While being questioned by Dr. Peter Silberman, Reese related some of his time with the Human Resistance which will have occurred before he was sent back in time, therefore the two events dated above and below would have occurred in this timeline, the timeline previous to that depicted in The Terminator, though shown in the movies future-war sequences.
2027
Kyle Reese, now a Sergeant (DN 38416) was reassigned to John Connors Tech-Comm unit.
[Source - The Terminator]
Although the dates are unknown, the attack on a Human Resistance base by a Terminator (to which Reese loses his photograph of Sarah Connor) and the destruction of an Hunter-Killer Tank during which a female Resistance soldier (possibly an iteration of Star from Terminator Salvation) was killed will have occurred before July 11th, 2029.
01:52am
A series 800, Cyberdyne Systems model 101 "Terminator" Infiltrator Unit was sent back in time to May 12th, 1984, using Skynet's Time Displacement Equipment, with orders to terminate Sarah Connor. Shortly afterward, Sergeant Kyle Reese (DN 38416) volunteered to follow the Terminator back in time to save Sarah J Connor from termination.
[Source - Terminator 2: Judgment Day, Revised Final Shooting Script]
To maintain this timeline Skynet would have sent a Terminator back in time to 1984. However, in this timeline, the Human Resistance, led by John Connor allegedly defeated Skynet and captured the TDE facility. After Reese volunteered to follow after the Terminator to protect Sarah from termination, John would have ordered a Terminator be reprogrammed to follow his orders, and together with detailed files on Miles Bennett Dyson, be sent back in time to June 8th, 1994.
Skynet sending a Terminator back in time to May 12th, 1984, to terminate Sarah Connor and the Human Resistance sending Reese back in time to protect Sarah from termination, maintains this timeline. However, the Resistance sending a reprogrammed Terminator back to June 8th, 1994 (and while the TDE was still active Skynet sending the T-1000) creates a new timeline, the Cinematic Timeline.
