Who is Mr. Motley from Perdido Street Station and what is their importance?

Mr. Motley is the insect-human creature who deals in dreamshit, the New Crobuzon equivalent of LSD combined with heroin. Motley possesses multiple mouths, and he is capable of speaking out of several of them at the same time. Over the course of the story, Motley hires Lin to create a sculpture of himself. He later has her executed because he believes her to be involved with a plot to take away his customers.