A "prodigal son" is a backwards or wayward male offspring who rebels against familial expectations and journeys into the world to seek their fortune, returning only with reluctance and/or repentance. Eldon Tyrell refers to Roy Batty as his "prodigal son" when the renegade replicant confronts his maker in search of a longer lifespan; Roy was created by Tyrell, sent into the universe to serve as a soldier, and then returns to him only because he is dying.
The phrase orginates in a parable found in Luke 15. He not only returns to confront Tyrell (his "Father") via Sebastian, but at the end joins him in death. See also Religion