Skynet is a fictional artificial neural network-based conscious group mind and artificial general superintelligence system that serves as the main antagonist of the Terminator franchise.
In the first film, it is stated that Skynet was created by Cyberdyne Systems for SAC-NORAD. When Skynet gained self-awareness, humans tried to deactivate it, prompting it to retaliate with a nuclear attack, an event known as Judgment Day. John Connor forms a human resistance against Skynet's machines in the future, which include Terminators, and ultimately leads the resistance to victory. Throughout the film series, Skynet sends various Terminator machines back in time to try to kill Connor to ensure Skynet's victory.
The system is rarely depicted visually in any of the Terminator media, since it is an artificial intelligence system. In the 2009 film Terminator Salvation, Skynet made its first onscreen appearance on a monitor primarily portrayed by English actress Helena Bonham Carter and other actors. Its physical manifestation is played by English actor Matt Smith in the 2015 film Terminator Genisys. In addition, actors Ian Etheridge, Nolan Gross and Seth Meriwether portrayed holographic variations of Skynet with Smith.
In Terminator: Dark Fate (2019), Skynet has been erased from existence after the events of Terminator 2: Judgment Day (1991), and another AI, Legion, has taken its place. In response, Daniella Ramos forms the human resistance against Legion, which prompts Legion to attempt to eliminate her from the past as Skynet tried with Connor.