He was portrayed by the late Colin Blakely in 1974 film adaptation, and by Willem Dafoe in the 2017 film adaptation. In the 2006 video game adaptation, Hardman is voiced by Nolan North, who also voices Edward Masterman and Dr. Constantine in the game.
In the novel
Hardman is a private detective working for McNeil's Detective Agency in New York. Whilst not having any direct relations to the Armstrong Family, Hardman did have an indirect one due to being the lover of the late Susanne Michel, who was Conductor Pierre Michel's daughter and only child, as well as the Armstrong Family's maid.
After the death of Daisy Armstrong, Susanne was falsely accused to be Cassetti's accomplice due to being manipulated by the criminal, and she tragically committed suicide in prison, before her name was cleared. Upon Cassetti's release from the court, Hardman joined Linda Arden's cause to eliminate Cassetti and avenge his victims for the sake of justice. He went on-board the Orient Express and tracked down Cassetti, who now went by the name of Samuel Ratchett.
At the time, Hardman (or so he claimed) was chasing a couple of criminals throughout Europe, which ended in Istanbul. He wired his boss, and received instructions to return to New York. Before he could, however, Hardman received a letter from Ratchett, telling asking him to report to Ratchett's suite at the Tokatlian Hotel.
Ratchett had suggested that Hardman take the compartment next to his but he could only get compartment 16, at the end of the coach. Ratchett had asked him to look out for a small dark man with a womanish voice. Ratchett also told him he didn't think it would be the first night, more likely the second or third. With regards to Ratchett engaging Hardman to protect him, how much was true was never confirmed in the book.
After Ratchett's death, Poirot interviewed Hardman, who revealed his true identity and showed this letter to Poirot. At the interview, Ratchett showed Hardman the threatening letters that he had received and suggested that he board the same train to Paris as a bodyguard.
When Poirot told Hardman that Ratchett was Cassetti, he said he did not recognize the face as he had been out west during the time of the crime. He also did not know any small dark men connected with the Armstrong case. On the train he had slept in the day and watched at night but nothing happened on the first night. On the second night, he did not observe any strangers pass his compartment.
Nevertheless, upon some observation, Poirot managed to discover that Hardman fell in love with a French woman whom he tragically lost, when he shed tears over Poirot's compliments over French ladies. Poirot soon deduced that the said lover of Hardman was Susanne Michel and discovered Hardman's role in the case. After the denouement, Hardman, alongside all of his accomplice, were spared by Poirot.
In the 2017 film
In the 2017 version, Hardman first appeared under the disguise of an Austrian-German Professor of Engineering, and was under the alias of Gerhard Hardman. This persona had showed a great amount of demeaning racist views. He also constantly showed obnoxious bias against certain people like African-Americans, Italians, Spaniards and Belgians, which visibly offended several passengers like Poirot, Mary Debenham and Dr. Arbuthnot.
However, this was revealed to Hardman's own pretense to make outsiders believe him and others were strangers. It was revealed that Hardman was never a racist and was actually a nice person apologized to Poirot for his offending attitude to put up a ruse. Poirot also revealed Hardman's true identity as a former police and confisicated his gun.
During the denouement, Poirot revealed every other passengers in the compartment, with the exception of Bouc, had took part in Cassetti's murder. Since he could not lie, Poirot decided to give all of them in to the authority unless they could kill him, before he handed Hardman's confisicated pistol to Linda Arden, urging her to kill him if she and her accomplices wanted to go free.
However, Arden refused to kill Poirot and claimed she already died with Daisy, before she tried to kill herself, much to Poirot's surprise and everyone else's horror. Nevertheless, Poirot already emptied the pistol and Arden failed her suicide, which revealed to be just a test set by Poirot to see if they really tried to pursue justice.
Hardman was last seen on the train, sitting in a chair, with a sad expression on his face as Masterman consoled him. He and his accomplice were all spared by Poirot, who gave them all a heartfelt speech and departed.
- Hardman was omitted in both the 2001 television film version and the 2010 adaptation from Agatha Christie Poirot. In the latter version, his role as the lover of Michel's daughter (renamed as Francois Michel) was refitted on Antonio Foscarelli.