Posted by modwiz
(here)
James Horak has a take on the Greys' that I am comfortable with. He calls them extra biological entities or EBE's. He says they are soulless programmed bots sent to scout the universe. They are, in essence, 'wet computers'. With the ability to repair each other and no real lifespan limit they could go and explore the galaxy. Without wormhole technology intergalactic travel was a very time consuming affair. The EBE's were the ticket. Apparently they were sent out so long ago that some of the races that sent them out have gotten newer space traveling technology or died out. This makes the Greys rebels without a cause or mission other than to stay around and keep operating. It seems endless self repair and sustaining themselves was part of the programming, but decommissioning was not.
I'll bet Isaac Asimov would be intrigued by this.