Terminator 3: Rise of the Machines (2003)

A machine from a post-apocalyptic future travels back in time to protect a man and a woman from an advanced robotic assassin to ensure they both survive a nuclear attack.
 
Director:  Jonathan Mostow
Writers:  John Brancato (story by), Michael Ferris 
Stars:   Arnold Schwarzenegger, Nick Stahl, Kristanna Loken