Elihu (a.k.a, the "Czar of Poisonville") is the father of the murdered Donald Willsson. He's a hot-tempered forty-year-old man who owns every important business in Personville.
During World War I, there was a labor strike at the Mining Corporation, and Elihu hired a group of thugs to control the strike. But after the strike was terminated, the thugs didn't want to give up their power, and Elihu couldn't openly break with them since he had hired them in the first place. Fast forward to the late twenties and the arrival of the Op, and now Elihu wants to hire the Op to clean up Personville. Elihu writes the Op a $10,000 check and lets him take whatever steps are necessary to rid the city of gangsters. It sounds like a nice thing to do, but if we're being perfectly honest, Elihu is shady like the rest of 'em.
Donald is the one who sends for the Op, but he's whacked before we get a chance to meet him. As the editor of the Herald newspaper, Donald had plans to publish pieces exposing the corruption of Personville. He is described as an honest, morally upright crusader, and the implication is that he had no knowledge of his father's criminal dealings.
The Op figures out that Albury murdered Donald out of jealousy. When Albury saw that Donald had written out a check to Dinah, Albury mistakenly believed that he was losing Dinah to Donald. But in fact, Donald was paying Dinah for information on the mobsters to publish in his newspaper. He's really just about the only honest man in Personville, so it figures that he's dead before we ever meet him.
Mrs. Willsson is Donald's wife. She meets with the Op the day he arrives and tells him that Donald isn't at home. Halfway through their conversation, she receives a phone call and steps out mysteriously. She's gone for forty minutes, and when she returns, the Op notices that her shoes look like there's blood on them. After Donald's dead body is found, Mrs. Willsson seems to be a prime suspect.
The Op and Noonan go to question her and she finally breaks down and says that she had received an anonymous call, telling her that Donald was at Dinah's house. She drove to Dinah's and also saw Whisper there. Mrs. Willsson sees her husband leaving Dinah's house when he's suddenly shot down in the middle of the street. She runs over to the body, but Whisper pulls her away and convinces her to leave. The Op later figures out that Albury is the one who made the anonymous phone call and killed Donald. Mrs. Willsson disappears from the rest of the novel.