Who is Manus Visser from A Coffin for Dimitrios and what is their importance?

Visser is one of the men who run Dimitrios's drug operations, dealing with clubs and bars on the distribution end. Visser goes after Dimitrios after he gets out of jail, and he blackmails Dimitrios. Dimitrios stabs Visser and plants a false identification card on him, so the police will think Dimitrios is dead. The body that Latimer sees in the morgue in Turkey is actually Visser.