Who is Gene Doolie from Junky and what is their importance?

Gene Doolie is a junky. He buys drugs from Bill when he is peddling them in New York City. Bill describes Doolie as a scrawny, little Irishman, who behaves like a homosexual pimp. Doolie is a known police informer and habitual collaborator. His voice is described as a shrill, grating whine. Doolie is devoid of empathy and personality; Bill describes him as a hostile, intrusive force.