I'm not sure if I'm remembering this correctly, but I think Sarah mentioned some guy in T1 (I think it's when she is getting ready with her friend to go out). I assume this guy would probably end up being with Sarah if Kyle didn't arrive and therefore possibly being John's dad. Don't quote me on that though.
The issue of who John Connor's "original" father was has always been a point of contention on this board. Before "T3" came out, one could argue that Kyle Reese had always been John's father; that was, it seemed, the paradox driving the first film - just as, in "T2", there appeared to be another paradox in that it was the Terminator coming back through time in the first film that led to the very creation of Skynet (until, of course, Sarah Connor and the T-800 intervened).
"T3", however, appeared to disprove this second paradox, since Judgement Day still took place - the actions of the Connor family merely delayed it; as the T-800 noted in that film, the nuclear holocaust was "inevitable". Therefore, if this second paradox was seemingly proved false, then why not the first one as well? Perhaps Kyle Reese was not, in fact, John Connor's father in the timeline prior to the events of "T1"? I imagine, however, that this will remain a subject of much debate amongst Terminator fans, and that the movies will never provide us with a definitive answer either way ...
Ahnold Sez: (From "The Expendables 2"): "My *shoe* is bigger than this cahr!"
According to the first Terminator movie and story line the man that Sarah was dating; Stan Morski should be the first original true biological father of John Connor, or another man she was dating/unknown around the time resulting in her being a single mother. However, there is no evidence that Sarah and Stan were actually involved, only that they had a date (which he canceled). Some how later in life John Conner survived “Judgment Day” to become a resistance leader and sent Kyle Reese back in time to protect his mother and save her so he could be born. This created the paradox or alternate present and future life for the new John Conner father by Kyle Reese from the future. This would mean Kyle Reese was not John’s original father but became his father and changed the course of the future. What do you think out there?
The first one is not so spoilerish, I tagged it just in case. The second one, however, I wouldn't go near if you have not seen Salvation yet.[SPOILER - highlight to read]: This was addressed, in a way, in Salvation.
[SPOILER - highlight to read]: If Kyle Reese died, John was worried about the future being changed and him not existing anymore.
The only thing thats with you your whole life is complete and utter darkness.