A human and his two servitors came to earth to hunt down bad guys.
Three laws of robotics:
The First Law: A robot may not harm a human being, or allow a human being to be harmed;
Second Law: Unless the First Law is violated, robots must obey human orders;
Third Law: Without violating the First and Second Laws, a robot must protect itself.
And, Rule Zero.
Concept: Interstellar Detective