Rider of Fate's End

I thought about what the story behind this character would be, and a Terminator-like story where the robot is sent back in time to either assassinate or protect an important historical figure was a natural fit, except rather than mere decades, he is instead sent back centuries to a medieval fantasy world. Alternatively, he could be some sort of time policeman sent to either maintain or alter the timeline as directed by his superiors, or even a free agent that stalks the timeline for anomalies, acting on inscrutable motives that only he understands.