Zachariah Osborne is the main antagonist of Agatha Christie's 1961 detective novel, The Pale Horse.

Osborne is a pharmacist who is behind a string of serial murder and conspiracy he had committed, as well as the true leader of the Pale Horse organization. He used the women at the Pale Horse, Mr. Bradley and Customers' Reactions Classified to hide his actions. He is the arch-enemy of Mark Easterbrook and Ariadne Oliver.

He was portrayed by Tim Potter in the 1997 ITV film adaptation, by JJ Feild in the 2010 adaptation from Agatha Christie's Marple (who also portrayed Simon Doyle in Agatha Christie's Poirot), and by Bertie Carvel in the 2020 adaptation, who also portrayed Agatha Trunchbull in Matilda the Musical during its 2010-13 run.


Zachariah Osborne was a pharmacist who ran an organized crime within the Pale Horse hotel conspiracy. He used the black magic element and manipulated the mediums led by Thyrza Grey to choose his victims. He used the black magic as a piece of misdirection on his part, and committed murder via replacing products the victims had named in the CRC (Customers' Reactions Classified) survey with poisoned ones.

It should be noted that he poison Osbourne used was thallium, a fatally poisonous metal that is tasteless and have affects of making its victim having hair falling down, before the poison slowly killed them when there was a certain dose.

At the start of the story, Mrs. Davis, an expelled member of the criminal organization who was also poisoned, confessed to her friend Father Gorman before her death and handed him a list of Osborne's victims to him. After Mrs. Davis' death, Father Gorman hid the list in his shoe and went for Scotland Yard, but was attacked and killed by Osborn, who was stalking him, in the meantime when Mark became wary of a schoolgirl dying with her hair being pulling out of her head, during a fight just a few days ago.

Mark later received the list from the police and started his investigation alongside Mrs. Oliver and other allies. While pretending to assist Mark during his investigation, Osborne later framed Mr. Venable for the crime and described to Mark, in order to drew suspicion elsewhere. In spite of his correct description over Mr. Venable's scarred face, he was not aware from the beginning that Mr. Venable was crippled for real due to polio, leading to Osborne's final exposure.

Osborne was resposible for the death of several guests in the Pale Horse hotel, including the death of Lady Hesketh-Dubois, Mark's godmother. Because of the public's lack of knowledge of thallium poisoning at the time, their deaths was mistaken and reported as illness and natural causes.


Real-life Influences

The Pale Horse is notable among Christie's books as it is credited with having saved at least two lives after readers recognised the symptoms of thallium poisoning (the killer's main method of murder) from its description in the book, as well as inspiring several case of murder with thallium as murder weapons (inspired by Osborne's actions).

  • For instance, in 1971, Graham Frederick Young, known as the "Teacup Poisoner" who had poisoned several people, three fatally, was caught thanks to this book.
  • In 1975, Agatha Christie received a letter from a Latin American woman, who had saved another woman from slow poisoning by her husband, since she recognised the symptoms of thallium poisoning through reading the novel.
  • In 1977, a 19-month-old infant from Qatar was suffering from a mysterious illness which was caused by thallium poisoning. After the baby was flown to London, Marsha Maitland, had recognized the real reason behind such sickness and saved its life, thanks to the knowledge from The Pale Horse she had been reading.
  • In 1988, a Mensa Club member named George Trepal put thallium into a Coca-Cola Classic bottles eight-pack and poisoned his neighbours, Pye and Peggy Carr and their children. Peggy Carr was killed while the others survived the attack. It became known as the Mensa Murder, and The Pale Horse was cited to be a possible inspiration for the killer's method.

In Adaptations

  • In Agatha Christie's Marple, Osborne's first name was changed into Paul, and his occupation was changed into being a member of a Sales Office, not a pharmacist.
    • Other modifications included Osborne being tricked into his exposure by Miss Marple, Mark, Mr. Venable and Inspector Lejeune.
    • After being revealed as the culprit, Osbourne attempted to poison Miss Marple after being exposed, but it failed since Marple already discovered his plot. She revealed it was courtsey to a mistake he made in not observing her sense of order, and managed to trick him into believing she was dying from poisoning as well with the comb from a victim.
  • In the 2020 miniseries adaptation, Osborne was killed by Mark during their final confrontation. In this adaptation, he ran a metal shop.



Agatha Christie's signature Villains
(Non-Poirot & Non-Marple)

Tommy and Tuppence Beresford
Conspiracy (Mr. Brown, Mr. Brown's decoy & Mr. Whittington) | Elise | Sir Phillip Stark | Mrs. Lancaster | Miss Bligh | N & M

And Then There Were None
Anthony James Marston | Mrs. Ethel Rogers | General John Gordon Macarthur | Mr. Thomas Rogers | Emily Caroline Brent | Justice Lawrence John Wargrave | Dr. Edward George Armstrong | William Henry Blore | Philip Lombard | Vera Elizabeth Claythorne | Isaac Morris

Other Mystery Stories
The Man in the Brown Suit (1924): Sir Eustace Pedler
The Sittaford Mystery (1931): Major Burnaby
Why Didn't They Ask Evans? (1934): Roger Bassington-ffrench | Moira Nicholson
Death Comes as the End (1944): Yahmose | Nofret | Satipy | Sobek | Ipy | Henet
Towards Zero (1944): Nevile Strange
Sparkling Cyanide (1945): Ruth Lessing
Crooked House (1949): Josephine Leonides
Destination Unknown (1954): Thomas Betterton
Ordeal by Innocence (1958): Jacko Argyle | Kirsten Lindholm | Rachel Argyle
The Pale Horse (1961): Zachariah Osborne
Endless Night (1967): Michael Rogers | Greta Andersen

Adaptational, Homage & Non-Canonical
Bellamy Gould | Leo Argyll | Ransom Drysdale

MarpleLogo Villains

Anne Protheroe | Charlotte Blacklock | Dr. James Kennedy | Elvira Blake | Lance Fortescue | Josie Turner | Lucky Dyson | Mark Gaskell | Tim Kendall

Villainous Victims
Colonel Protheroe | Ella Zielinsky | Giuseppe | Heather Badcock | Lucky Dyson | Rex Fortescue | Victoria

Jane Helier | Lady Sedgwick

ITV Series Exclusive
Original Characters & Adaptational Culprits
Brigit Milford | Tilly Rice
Originated from non-Marple stories
Adelaide Jefferson | Charles Burnaby | Helen Kennedy Halliday | Greta Andersen | Jacko Argyle | Kirsten Lindholm | Rachel Argyle | Michael Rogers | Miss Bligh | Moira Nicholson | Mrs. Lancaster | Nevile Strange | Paul Osborne | Roger Bassington-ffrench | Sir Phillip Starke

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