Hercule Poirot is a famous Belgian detective traveling from Istanbul to Europe. He is highly observant and methodical, relying heavily on psychological profiling and logical deduction rather than just physical evidence. He is called upon to solve a complex locked-room mystery when his train becomes stranded in a severe snowstorm and a passenger is found dead.

M. Bouc is the Belgian director of the Compagnie Internationale des Wagons Lits train company. He recruits Poirot to solve the case in order to protect his company's reputation from scandal. He acts as an eager sounding board during the passenger interrogations, though he frequently jumps to conclusions based on national stereotypes.

Dr. Constantine is a Greek doctor traveling aboard the stranded train. He examines the victim's body and assists Poirot and M. Bouc with the subsequent passenger interviews. He offers essential medical insights regarding the crime scene and the varied nature of the victim's wounds.

Mr. Ratchett is an older, wealthy American passenger traveling with a secretary and a valet. He receives multiple death threats and attempts to hire Poirot for protection before being found fatally stabbed in his locked compartment. His brutal death launches the central investigation.

Hector MacQueen is an American man working as the personal secretary to Mr. Ratchett. He handles travel logistics and claims to know very little about his employer's background or the source of the threatening letters. He appears straightforward and cooperative during Poirot's initial questioning.

Edward Henry Masterman is an English valet serving Mr. Ratchett. He maintains a highly composed, expressionless demeanor typical of a well-trained servant. He shares a second-class compartment with an Italian passenger with whom he frequently clashes due to cultural differences.

Mrs. Hubbard is an older, highly talkative American matron traveling in a compartment adjacent to the murder victim. She frequently voices her anxieties about her safety and insists that a strange man was hiding in her room on the night of the crime.

Greta Ohlsson is a Swedish woman traveling on the Orient Express who shares a compartment with Mary Debenham. She is easily flustered and inadvertently opens Mr. Ratchett's door by mistake while looking for an aspirin on the night of the murder.

Princess Dragomiroff is an extremely wealthy, elderly Russian aristocrat traveling on the train. She demands respect and requires the frequent attention of her personal maid due to poor health and chronic insomnia.

Hildegarde Schmidt is a German lady's maid working exclusively for Princess Dragomiroff. She is unquestioningly devoted to her employer, waking late at night to provide massages when the Princess cannot sleep.

Count Andrenyi is a Hungarian diplomat traveling in the first-class section with his wife. He acts as a fierce shield for his spouse, attempting to keep her completely isolated from Poirot's questioning by insisting they slept through the entire night.

Countess Andrenyi is the young, elegant wife of Count Andrenyi. She claims to have taken a sleeping draught on the night of the murder, leaving her completely unaware of the surrounding commotion in the adjacent compartments.

Colonel Arbuthnot is an English military man in his forties or fifties returning from India. He is stoic, prefers the company of fellow English passengers, and firmly believes in traditional systems of law and trial by jury.

Cyrus B. Hardman is a flashy American passenger who reveals himself to be a private detective from New York. He claims Mr. Ratchett hired him to watch out for a dangerous, high-pitched man who was actively threatening his life.

Antonio Foscarelli is a large, expressive Italian man traveling on the Orient Express. He shares a compartment with the English valet Masterman and becomes an immediate suspect to M. Bouc based entirely on xenophobic stereotypes regarding his nationality.

Mary Debenham is a poised, cool-headed young British governess in her late twenties. Poirot notes her extreme self-possession and harbors early suspicions regarding a cryptic, hushed conversation he overhears her having.

Pierre Michel is a French conductor for the Compagnie Internationale des Wagons Lits. He is responsible for the specific carriage where the murder occurs and provides essential timeline details regarding the passengers' movements throughout the night.