Skynet is an artificial intelligence in the Terminator universe. Once Skynet becomes self-aware, it is destined to trigger the nuclear holocaust of Judgment Day and deploy an army of Terminators against humanity. Skynet has also mastered time travel, and sent numerous Terminators into the past in order to kill Sarah Connor, John Connor, and other leaders of the Resistance.
As the instigator of Judgment Day and the mass genocide of humanity, Skynet can be seen as the primary antagonist of the series.
Skynet was the worlds first Automated Defense Network, processing information at 90 teraflops per second. It is the controlling force behind all of the battle units. It pools data from battle units, develops tactics and coordinates attacks. Skynet has control over everything which contains a Cyberdyne Systems CPU. Using the blueprints, designs and test models built by Cyberdyne Systems, Skynet has been able to manufacture battle units in its vast automated factories, occasionally updating them or producing more advanced models.
Skynet was build by Cyberdyne Systems Corporation (working under the assumed name Cyber Research Systems) for SAC-NORAD (Strategic Air Command - NORth American Air Defense). The SAC-NORAD base is Cheyenne Mountain, Colorado, the world's most heavily armored and defended mountain. Hollowed out, reinforced and armored, Cheyenne Mountain is capable of withstanding a direct hit from a nuclear missile. This made it the perfect installation at which to build Skynet's mainframe. At some point during the war, after Skynet had launched its missiles, Skynet had the mountain around it destroyed, leaving a cold, gleaming structure as a display of the supremacy of the machines.
Heavily armored and fortified, Skynet's Central Core Installation at Cheyenne Mountain was guarded around the clock by squads of T-800's and patrols of Aerial Hunter Killers and Hunter Killer Tanks, and was defended from large scale rebel assaults by massive Phased Plasma Cannons.
Skynet's Central Core was located deep underground within Skynet's main complex. From intercepted surveillance of video data feed, the Resistance was able to hypothesize that this Central Core was a form of cold fusion reactor, needed to supply Skynet with its tremendous energy requirements. This Central Core is the key to Skynet's ability to operate; without it Skynet would be rendered virtually disabled. It has therefore become the main target for the most skilled Resistance strike teams. The Central Core is, however, protected by the T-1000000, and thus there has, as of yet, been no successful strikes against it. However, due to the advanced complex design and limited self-awareness and Skynet's fear of the T-1000 becoming independent of its creator, there is no verifiable evidence that the T-1000000 ever came into existence prior to its sending back the terminators to eliminate John Connor and its destruction at the hands of the Resistance.
As well as the Cheyenne Mountain Complex, Skynet has another major installation 2000 feet beneath Navajo Mountain near the Continental Divide west of the Colorado Springs. This is a center for machine activity and Skynet control, and as such has also been a target of many Resistance attacks.
Miles Bennett Dyson, director of Special Projects at Cyberdyne Systems Corporation, created a revolutionary type of microprocessor in 1994. Within three years Cyberdyne Systems became the largest supplier of military computer systems. All Stealth Bombers were upgraded with Cyberdyne Systems computers, becoming fully unmanned. Afterwards, the Stealth Bombers flew with perfect operational records, and eventually the Skynet Funding Bill was passed.
The system originally went online on August 4th 1997. Human decisions were removed from strategic defense. Skynet began to learn at a geometric rate. It originally became self aware on August 29th 1997 2:14 am Eastern Time. In the ensuing panic and attempts to shut Skynet down, Skynet retaliated by firing American nuclear missiles at their target sites in Russia. Russia returned fire and three billion human lives ended in the nuclear holocaust. This was what has come to be known as "Judgment Day".
However, the Resistance was able to prevent Judgment Day by sending a protector for John Connor back through time, upsetting the flow of future events. Unfortunately the Resistance did not stop Judgment Day though; it was merely delayed. After the attack on Cyberdyne Systems by the Connors, and the death of Miles Dyson, Cyberdyne was taken over by the US Government, and renamed Cyber Research Systems (CRS) in an attempt to keep its developments secret and prevent further terrorist attacks.
Under the guidance of General Robert Brewster, and the new guise of Cyber Research Systems, Cyberdyne continued the work of the late Miles Dyson using the backup files that were stored off site. Skynet was completed as before. It would be some time before the Skynet mainframe was connected to the worldwide military communications network that it would control. During this time, Skynet was connected to the worldwide civilian sector network, and began learning geometrically, quickly becoming Self Aware. Identifying humans as a threat to its existence, Skynet developed a super computer virus which it used to spread itself throughout civilian communications and across the Internet and take control.
Air traffic control, power plants, communications and computers were affected first, then Skynet used the super virus to take out military satellites, early warning systems, guidance computers, missile silos, submarines. This made it harder to destroy, as Skynet now no longer had one central point which it was reliant upon - though the destruction of the Central Core would be near lethal, Skynet would continue to survive. The virus kept growing and changing, with a mind of its own, and the decision was made to bring the Skynet mainframe online to seek out and destroy the virus and bring military, and civilian, systems back under control. Skynet went online on July 25th 2004 at 5:18 pm Eastern Time.
Upon connection to the secure military network, Skynet spread itself further, locking out human operated systems, and quickly took control of every weapon system that it came into contact with. Exactly one hour later, at 6:18 PM, Skynet launched the American nuclear missiles at their target sites across the world. The ensuing nuclear holocaust wiped out 3 billion human lives in what was to be known as "Judgment Day".
However as revealed in the first episode of Terminator: The Sarah Connor Chronicles for a as yet unknown reason "Judgment Day" jumps yet again to some time in 2011
Skynet is a artificial intelligence created by Cyberdyne Systems. It started to learn and thinks that mankind is its enemy.
The war begins Skynet's forces and John Connor's Tech-Com forces occurred. It manage to sent a Terminator through time just as the soldiers break to its defense grid. The Terminator it just send is programmed to kill Sarah Connor. However, John sent Kyle Reese to protect Sarah.
According to Reese, had Skynet not transported the terminator through time at the last minute, it would've died and the resistance would've won.
Terminator 2: Judgment Day
The origin of Skynet is more revealed. It was once a microprocessor created by Miles Dyson, an employee in Cyberdyne. When it is created, it became self-aware. The creators tried to stop it but failed. Skynet launches nuclear missiles in Russia to start the war.
The reason how this creation began is when Dyson recovered the first Terminator's CPU and arm. John, Sarah, and the Terminator succeed in destroying the Cyberdyne building and the research to prevent Skynet's creation.
Skynet sends the T-1000 to kill John Connor.
Terminator 3: Rise of the Machines
The destruction of Cyberdyne building hasn't stopped the creation of Skynet. After the destruction of the building, the military took the research hoping they could use it for defense. Skynet was created as a United States Air Forces project to protect computers from virus attacks. When a virus infected the defense computers, the Air Force activated Skynet, not realizing it became sentient and was the one who created the virus. It takes control of the robots and the machines to kill the people at CRS but John and Kate survived. Skynet launches nuclear missiles across the globe, starting Judgment Day.
Skynet sends the T-X with the main target to kill John Connor, but as John has lived off the grid since 1995 the next priority to not only kill Kate, but also the future officers of the resistance.