"There was a war.
And it devastated the Earth.
Our weapons and their weapons were unleashed against their makers by a third and unexpected player. The artificial intelligence which had been created to control the bombers and launch the missiles with their nukes and chemicals and germs... the computer entrusted with that grave responsibility one day decided to have done with the folly that was Man and create real order and real intelligence on the planet for the first time.
Humans were obsolete.
The cities fell and in the ruins the survivors were hunted down and slaughtered by the gleaming patrol machines, built by robots in the automated factories. Large groups were rounded up into camps where liquidation could proceed in an orderly and sanitary fashion.
Only one force opposed the cybernetic Reich. A single man, a man who rose out of the slag heap to organize the survivors against the pogroms, to resist the genocide, to storm the wire of the camps and smash their metal executioners into junk." --James Cameran, from the Terminator Original Script Treatment.
That man's name is John Conners and he was the leader of the resistance against the machines.
The machine that started it all was called Sky-Net and it was an artificial intelligence program developed by Cyber Dynamics Incorporated (Cyberdyne), also known as CRS (Cyber Research Systems) based on the blue prints of an assassinated scientist known as Dr. Miles Bennet Dyson.
On August 7, 1997, at 2:30 am in the morning, SKYNET achieved a new order of intelligence, it became sentient, and the rest is history.
ALTERNATE TIME LINES
Note: Due to the tampering of Sky-Net with time travel in a desperate attempt to thwart mankind's inevitable success in the war against it, several different parallel time lines were created in which certain key events were all slightly different. However, it was discovered that time has a way of healing itself and in each parallel universe that was created several key events always take place leading to a similar future in which Sky-Net is defeated in 2029.
1) May 12, 1984
T-800 sent back to kill Sarah
Sarah is protected by Kyle Reese
Sarah becomes pregnant
2) February 28th, 1985
John Connor is born
3) May 12, 1995
A T-1000 is sent back to kill John Connor
A T-800 protects him
The Terminator artifacts are destroyed
4) Despite these events, at some point between 1997 and 2003 Sky-Net comes on line and brings about a nuclear holocaust.
5) At some point Sky-Net begins creating Terminators to kill the remaining humans.
In each parallel universe the sequence and evolutionary progress of the Terminator androids is the same, producing the same exact models in each parallel universe, but the dates that the androids are first produced vary slightly with each parallel time line.
6) Late 2029
Skynet's defense grid is smashed
Two T-800s sent back in time (one is sent by Sky-Net to 1984 and one is sent by the resistance to 1995)
Prototype T-1000 also sent back to 1995
7) In all, Sky-Net's tampering brings about 7 alternate time-lines, but in the end the future always corrects itself and humanity always ends up defeating Sky-Net with the aid of a human leader named "Conners".