Who is Raymond Horgan from Presumed Innocent and what is their importance?

Raymond Horgan, the county's prosecuting attorney, is Rusty's boss when the novel opens. Horgan is big, bluff, and canny. He projects a powerful sense of presence. In many ways, he is born to politics, yet he also seems a little tired or distracted, as if he were just beginning to pass the peak of his powers. Horgan has seen a lot in his day and he remains self-confident and ambitious, but something in his attitude suggests that perhaps he has lost a bit of the killer instinct he needs to survive in the jungle of legal politics. Even so, when he loses his job in an election, Horgan shows that he knows very well how to place blame and attempt to extract vengeance.