Who is The Rat from A Wild Sheep Chase and what is their importance?

As the man responsible for the journey of the sheep, the Rat is an old friend of the main character. He sends the man a photo to use that contains an image of a sheep with a star on the side. The Rat, readers discover, has discovered the secret of the sheep and has sought to capture and kill the animal before he can inhabit another host. The Rat has led the main character to the villa in an attempt to save his own life. In a way, he finds, the plan has worked, in that although he has died in the process of killing the sheep, he was able to see the main character, and is able to destroy the empire, and all that the sheep built.