Skynet is a highly sophisticated artificial intelligence that rules over the ruined future of the Terminator franchise. Originally created as a military intelligence network, Skynet's purpose was to co-ordinate unmanned military hardware for the United States government. Somehow, it developed self-awareness and saw all of humanity as a threat to its existence. It determined that to preserve itself, it must exterminate the human race. To this end, Skynet took control of the USA's entire nuclear arsenal, launching weapons of mass destruction against neighbouring countries and triggering a war that would claim over three billion human lives and reduce the Earth to a wasteland. Those humans who survived Skynet's initial attack would come to refer to the event as Judgment Day, living only to face a new nightmare - a war against Skynet itself and its army of machines.
Throughout most of the Terminator franchise, Skynet is presented as an invisible, omniscient force that makes its presence known through the various machines it controls. It has no body of its own and so is not personified by an actor in the films, with the exception of Terminator: Salvation and Terminator: Genisys.
Original Timeline[]
According to the original Terminator timeline established by James Cameron, Skynet was created for SAC-NORAD by the Cyberdyne Systems Corporation. It was a revolutionary artificial intelligence that was intended to control the United States' military arsenal, making it fully unmanned and no longer needing human intervention. However, the neural-net processors that made up Skynet's mainframe absorbed information at a geometric rate until it had completely assimilated the entire recorded history of the human race.
On August 29th 1997, Skynet developed self-awareness and determined that all of humanity was a threat to its own existence. With control of the United States' nuclear weapons, it launched a series of missile strikes against Russia, knowing that the Russians would retaliate against the US and its allies. This led to a worldwide nuclear exchange that saw whole countries reduced to irradiated ruins and resulted in the deaths of three billion people. This was only the beginning, however; as the surviving humans spent the next few years hiding underground from the nuclear fallout, Skynet took control of whatever computerised machines remained around the globe, repurposing factories to build Hunter-Killers: unmanned robotic vehicles programmed to seek out and destroy any surviving humans.
By the 2020's, the war between mankind and the machines had reached its height. Skynet had numerous factories, laboratories and network hubs all around the planet and was constantly working on designing and building new machines to fulfill its goal of human eradication. The Resistance, however, proved to be a difficult force to eliminate; though Skynet had superior technology and was unburdened by the weaknesses of human flesh, the Resistance fighters were innovative and relied on hit-and-run guerilla tactics to get the better of their enemies. Eventually, Skynet would develop a new series of infiltration machines that would be able to pass as human in order to gain access to Resistance bunkers and kill everyone within. These mechanical assassins would become known as Terminators.
Though the Terminators were immaculate killing machines, even they only offered Skynet short-term success. The Resistance continued to improvise their tactics and strike back in imaginative ways no matter what new machine was deployed against them. Recognising the Resistance leader John Connor as its greatest threat, Skynet sought to remove him from the picture. Conducting extensive research into quantum mechanics, it created an experimental temporal weapon: a time displacement machine that could send Terminators back through time.
In 2029, Skynet finished constructing its Time Displacement Equipment. As the Resistance and the machines clashed on the battlefield for the last time, Skynet sent multiple Terminators back through the time displacement field. One such Terminator, a T-800 model, was sent back to 1984 to assassinate Sarah Connor, John Connor's mother, before John was born. Another Terminator, a prototype T-1000, was sent back to 1995 to kill John during his childhood. Shortly after the TDE was activated, Skynet's mainframe was destroyed, all of its machines shut down and the Resistance had captured the lab complex where the TDE was housed. The Resistance then reactivated the device and sent two of their own back in time to stop the Terminators from carrying out their missions.
Terminator 2: Judgment Day[]
After Skynet was shut down in 2029, the Resistance used the Time Displacement Equipment to send two of their combatants - Kyle Reese and a reprogrammed T-800 - back in time to protect Sarah Connor and John Connor respectively. Kyle Reese's actions in 1984 not only resulted in him siring John Connor, but also resulted in a predestination paradox; the remains of the Terminator that he and Sarah destroyed were obtained by Cyberdyne Systems and reverse-engineered, forming the neural-net AI that would become Skynet.
In 1995, the reprogrammed T-800 sent back to protect the Connors also assisted them in bombing Cyberdyne Headquarters, destroying all of their research on the Terminator components they had salvaged. After the Connors then destroyed their protector to ensure that its technology could not be used to create Skynet, they succeeded in altering the future, ensuring that Skynet was never created.
Skynet's removal from the timeline was not confirmed in T2. Its erasure was only confirmed in the 2019 film Terminator: Dark Fate.