Raffles is a minor character, but he's very important to the plot. He's the only person still living besides Mr. Bulstrode who knows about all the shady dealing of the Dunkirk family. Unfortunately for Bulstrode, Raffles is also the only living person who knows that Bulstrode lied about the whereabouts of Sarah Dunkirk so that he could marry her mother and take over the entire family fortune. Raffles appears in the middle of the novel and starts dropping hints about Bulstrode's past to anyone that will listen. His character basically serves as a device to move the plot forward. His death sparks the scandal that runs the Bulstrodes out of town and almost ruins Mr. Lydgate.