Wow, how is it possible that I've gone my entire life without knowing about this movie: Cyborg 2087 (1966)? The plot is surprisingly Terminatoresque:

Garth (Michael Rennie), a cyborg from the future, travels back in time to 1966 to prevent Professor Sigmund Marx (Eduard Franz) from revealing his new discovery, an idea that will make mind control possible and create a tyranny in Garth's time. He is pursued by two "Tracers" (also cyborgs) out to stop him.

Garth enlists the help of Dr. Sharon Mason (Karen Steele), Marx's assistant. He gets her to summon her friend, medical doctor Zeller (Warren Stevens) to operate on him, to remove a homing device used by the Tracers to track him. The local sheriff (Wendell Corey) also becomes involved.

Garth succeeds in defeating the Tracers and convincing Professor Marx to keep his discovery secret. Then, with his future wiped out as a result, Garth ceases to exist; the people who helped him do not even remember him.

Check out the trailer: