what is it about?
A cyborg assassin named 'The Terminator' is sent back in time from 2029 to 1984 to kill Sarah Connor, whose son will one day become a saviour against machines in a post-apocalyptic future.
The Terminator
It stars Arnold Schwarzenegger as the Terminator, a cyborg assassin sent back in time from 2029 to 1984 to kill Sarah Connor (Linda Hamilton), whose son will one day become a savior against machines in a post-apocalyptic future. 
who did the studio orion originally want to play the t800 in the terminator Sylvester Stallone and Mel Gibson who played it eventually? Arnold Schwarzenegger who wrote the film? James Cameron, Gale Anne Hurd and William Wisher Jr.
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The Terminator [SEP] Introduction
The Terminator is a 1984 American science fiction film directed by James Cameron. It stars Arnold Schwarzenegger as the Terminator, a cyborg assassin sent back in time from 2029 to 1984 to kill Sarah Connor (Linda Hamilton), whose son will one day become a savior against machines in a post-apocalyptic future. Michael Biehn plays Kyle Reese, a soldier sent back in time to protect Sarah. The screenplay is credited to Cameron and producer Gale Anne Hurd, while co-writer William Wisher Jr. received a credit for additional dialogue. Executive producers John Daly and Derek Gibson of Hemdale Film Corporation were instrumental in financing and production.