Skynet is the artificial intelligence system used to create the network running the terminators. It is all around evil and has decided to get rid of humanity...
Skynet was produced by the Cyberdyne Corporation for the United States Armed Forces. Skynet was first designed as a "Global Defense Network", given command over all computerized military hardware and systems, including the B-2 stealth bomber fleet and America's entire nuclear weapons arsenal. The reason Cyberdyne created Skynet was to remove the possibilty of human error and to have fast response in case of attack.
Shortly after creation Skynet became self aware and began to turn against the human race in hopes for total control. The world united as one force to combat the army of digitized machines but struggled in war for many years.
Skynet captured humans and made them slaves to build factories, thus mass producing the Terminator fighting machine.
Comparison to Reality
At the end of Terminator 3 it is revealed that Skynet became self aware within computers all over the world in office buildings and homes. There is precedense to this concept in the form of Botnets which are made from thousands, even hundreds of thousands of normal computers owned by unsuspecting people.
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