In these stories Isaac Asimov creates the Three Laws of Robotics and ushers in the Robot Age.
Earth is ruled by master-machines but the Three Laws of Robotics have been designed to ensure humans maintain the upper hand:
1) A robot may not injure a human being or allow a human being to come to harm
2) A robot must obey orders given to it by human beings except where such orders would conflict with the First Law.
3) A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.