Harold was described as "the perfect picture of a City gentleman and a director of important companies". He was tall and had a "neat erect carriage". He had dark hair going slightly bald on the temples, and a small black moustache. He lived at 43 Cardigan Gardens.
Harold married Lady Alice even though he was not in love with her, because he thought that her family and connections would be useful, and that her family would be nice relations for any sons they might have. However, they did not have any children. He and Alice had nothing in common, and had no particular pleasure in each other's company.
Harold had advised his sister Edith against marrying Bryan Eastley, saying that Bryan would probably not be any good in peace time, and would probably be barely able to support her. However, Edith had married Bryan anyway.
Harold told Lucy Eyelesbarrow that he was impressed with her ability, and asked her to call upon him in London. He felt that they could use someone of her outstanding ability in the firm, and promised her a very good salary with brilliant prospects.
The Crackenthorpe family, including Harold, was taken ill after eating a curry, and Dr Quimper was called to attend them. While Harold was recovering, Dr Quimper gave him some tablets to take at night.
When Harold returned home to London, he received a parcel containing a box of tablets that look like the ones he had been taking, with a piece of paper saying it was sent by request of Dr Quimper. Harold thought that Dr Quimper had said he would not need the tablets anymore, but he took two before going to sleep anyway, and was dead by the morning.
BBC's Miss Marple
In BBC's 1987 adaptation of 4.50 from Paddington, the character of Harold Crackenthorpe is played by Bernard Brown. Here his occupation is given as a banker and his bank is not strong financially. His wife, Lady Alice, is not shown on screen but Miss Marple apparently visits her in her house in London. There she learnt that Harold had an interest in ballet.
In this adaptation, Harold was also killed but in a different manner from the original novel. Here he is killed while out hunting on the Rutherford Hall grounds, apparently after his leg got caught in a trap. The police thought it might be suicide. Chief Inspector Duckham reasoned that Harold's finances were shaky. Some major creditors had advanced him loans on the basis that he stood to inherit from the Crackenthorpe fortune. The appearance of another legitimate claimant to the fortune such as from the "Martine" claiming to be Edmund Crackenthorpe's wife could cause one of these creditors to foreclose. Harold could have investigated and discovered that Anna Stravinska's real name was Martine Perrault. He then murdered her, believing she was Edmund's "Martine".
Duckham thought that Harold panicked after the discovery of Anna's body. He must have realised he would soon be caught and so committed suicide, but made it seem like an accident so that his wife could claim his life insurance. Miss Marple doubted this. Harold reminded her of Archibald Spate. They both had the same mannerism of fingering their cuff-links when nervous. Archibald Spate disliked his wife and when he died, did not leave her any money in his will. She had to go to court to assert her rights. To Miss Marple, Harold did not look like a man who loved his wife so much that he would think about ensuring that she would collect his life insurance payout. Moreover, the murder of Harold seemed to be done in haste, something that had to be done quickly after the discovery of Anna's body. Miss Marple theorised that Harold might have been killed to silence him. Harold had an interest in ballet. His house was filled with ballet memorabilia including a poster advertising the last English tour of the Ballet Maritska. Perhaps the killer feared Harold might know something about the background of Anna as a ballerina and this was potentially dangerous to him.
ITV's Agatha Christie's Marple
In ITV's 2004 adaptation of 4.50 from Paddington, the part of Harold is played by Charlie Creed-Miles. Here he is not as distanced from his wife as in the original novel. As opposed to spending her winters on the Riviera, here she comes down to Rutherford Hall with him. She appears quite fond of him, or at least holds up up in front of others. Harold has "a job for life" in his father-in-law's company which his wife tells others is a very responsible position.
Whatever feelings Harold's wife may have for him, they are not reciprocated. Later in the episode, it is revealed that, during the war, he had sexually assaulted Martine, his brother Edmund's wife. During the episode he also tries to assault Lucy Eyelesbarrow. Harold told Inspector Tom Campbell that he envied Edmund and his wife as well as his father and mother--they had such genuine love as couples. In this adaptation, Harold is not murdered. After he is cleared of suspicion in the murders, Tom Campbell tells his wife to take him home.
NHK's Agatha Christie's Great Detectives Poirot and Marple
In NHK's anime adaptation 4:50 from Paddington, the portrayal of Harold is close to the original. Here he is also killed after going back to London and from poison in his regular medicine. The character is voiced by Daisuke Ono.