Hercule Poirot, a recurring Christie character, has become one of the most famous fictional detectives. Poirot is a retired Belgian police officer turned private detective. As a private detective he tours Europe and the Mid-East solving murder mysteries. Because he is a private detective and has no apparent family, Hercule Poirot has a great deal of freedom. He is independently wealthy and the decisions he makes are not subject to law or otherwise. As exemplified in Murder on The Orient Express, Poirot does not always follow the law—he lets the real murderers go. This novel is one of two Christie books where the murder is let off. While Poirot does not always obey the law, he always abides his conscience and his sense moral law. "Moral Law" is somewhat like religious law or the law of God, it is a general sense of right and wrong that supersedes any man-made written laws. In the case of the Armstrong family, Poirot put moral law first. The private detective is an arbiter of morals; he has the power and the brains to fight evil.

Poirot is moral and intellectual superhero. He is quite clearly smarter than any of the other passengers, especially M. Bouc and Dr. Constantine. In the beginning of Section three, Christie includes a humorous comparison of the thoughts of the three men. While Poirot sits motionless thinking and concentrating on the case, M. Bouc's thoughts wander to the repair of the train and Dr. Constantine's waver into pornography. Poirot's greatest task as a detective is to be the smartest person around; he must intellectually defeat the murderer. The Armstrongs purposefully attempt to confuse and fool Poirot. They set an elaborate set of clues and misleading evidence to veer him from the truth, but Poirot still wins. From the time he sits down and "thinks" with Dr. Constantine and M. Bouc, Poirot knows the solution of the case—it is merely a matter of confirming his suspicions.

Poirot is a very likable character, despite his moral and intellectual greatness. He is over concerned with appearance, distracted by his moustache and has a liking for strong-willed British women (a.k.a. Ms. Debenham). He is rather short, slightly snobby and probably lonely at times. It is good Christie gives him cases so often. Hercule Poirot, through Christie's novels, is said to have aged to 105.