Raymond Chandler asserts that the main character in a hard-boiled detective story is "the hero. He is everything." This perspective, emphasizing the detective's central, nearly singular significance, is also applicable to Dashiell Hammett's Continental Op tales and novels. The Continental Op features in thirty-six short stories, some of which later formed the basis for Red Harvest and The Dain Course (1929). Unlike the master detective in classic mystery stories, the Op is a detective agency employee assigned various cases. He is short, stocky, overweight, and not conventionally handsome. Hammett intentionally left the Op without a first name to break away from the personality cult associated with traditional detectives and to depict him as a model of the working-class hero—anonymous, uncelebrated, yet deriving personal pride and loyalty from his work. In many respects, the Op is Hammett's alter ego; he has developed an existential moral code that guides his actions more than societal or legal rules in a corrupt world. Drawing from the American Western tradition, he is both drawn to and cautious of women; he is a solitary figure, unmarried, with no family or social ties mentioned. His moral compass is largely shaped by his job's demands, making him a simpler precursor to Sam Spade from The Maltese Falcon (1930). Like most hard-boiled detectives, his skills are physical and practical, contrasting with the intellectual, abstract reasoning of classic detectives.

Another key character in Red Harvest is Personville, the novel's social backdrop. The town's residents are entirely characterized by its pervasive moral decay. They display varying degrees of moral corruption, and aside from Elihu Wilsson, they lack depth. Donald Wilsson, whose murder sets the plot in motion, is the town's only relatively honest individual. The others, such as Max "Whisper" Thaler, Police Chief Noonan, and Dinah Brand, are mere puppets striving to become puppet masters, themselves ruthlessly manipulated by Elihu Wilsson's forces and the Op.

The novel's extensive character list highlights the widespread corruption in America. Brief glimpses of minor corrupt figures, irrelevant to the plot, suggest that greed and immorality extend beyond the main characters. In his later novels, Hammett reduces the number of characters but continues his relentless critique of American society and human nature.