Law Zero: A robot may not injure humanity, or, by inaction, allow humanity to come to harm

Law One: A robot may not injure a human being or, through inaction, allow a human being to come to harm.

Law Two: A robot must obey the orders given it by human beings except where such orders would conflict with the First Law.

Law Three: A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.

By Isaac Asimov