For the 1986 tribute anthology Foundation's Friends Harry Harrison wrote a story entitled, simply, "The Fourth Law of Robotics". This Fourth Law states:
"A robot must reproduce. As long as such reproduction does not interfere with the First or Second or Third Law."
In the book a robot rights activist, in an attempt to liberate robots, builds several equipped with this Fourth Law. The robots accomplish the task laid out in this version of the Fourth Law by building new robots who view their creator robots as parental figures.
Harrison's famous character The Stainless Steel Rat (James DiDriz) makes a guest appearance in this title.