Who is Lanik's Double from A Planet Called Treason and what is their importance?

Lanik's double, severed from Lanik's body, is taken in by the Nkumai, who train him in deep hatred of Muellers and Lanik. He goes around all the lands killing, maiming, burning, raping and torturing all in the name of Lanik, who is not even there. Everyone hates him. Lanik's double learns the secrets of Andersons, kills Dinte, and eventually takes over the leadership of Mueller, which the real Lanik is glad to give him after he heals him of his radical regeneration.