Monsieur Bouc, the director of the Compagnie Internationale des Wagon Lits, is an old friend of Poirot’s from their days of service in the Belgian Police Force. Reuniting coincidentally as Poirot looks to return to London on the Orient Express, Bouc becomes a key companion for the detective as he sets out to solve the case of Ratchett’s murder. Bouc, along with the coroner Dr. Constantine, is present through every step of the investigation, offering opinions and insights as new information emerges. Unlike Poirot, however, he quickly jumps to conclusions and struggles to see beyond the limits of his own biases. For the longest time, Bouc strongly believes that the Italian man, Antonio Foscarelli, is the murderer simply because he buys into false stereotypes associating Italians with violence and knives. He also clings to the assumption that Mary Debenham could not possibly be involved in the crime because she is charming and unemotional, traits which ultimately allow Poirot to identify her as the mastermind behind the plan. Given how often Poirot cleverly proves Bouc wrong, his frequent exclamations of surprise render him a rather comedic figure. Bouc’s simpler perspective makes Poirot’s investigative process and subsequent unraveling of the mystery appear even more impressive, and this contrasting dynamic adds to the rhythm of the novel as a whole. 

Beyond serving as a humorous foil to Poirot’s meticulous and thoughtful character, Bouc has the final say in what kind of justice they honor at the end of the novel. Poirot may offer two different solutions to the mystery, one believable enough for the police and the other the truth, but Bouc is the one who decides that the passengers on the train were justified in their collective killing of Mr. Ratchett. The power that he has to make such a moral judgement adds a layer of depth to his otherwise lighthearted character. He has the same background in police work as Poirot, meaning that he has familiarity with the legal system, but he no longer has a hand in it. This position, along with the fact that the reputation as the director of the train company is on the line, gives Bouc the sense of moral freedom required to disregard the law in favor of true justice.