Franklin is a wealthy, cosmopolitan gentleman who has recently returned to England after extensive travel abroad. He brings his uncle's controversial inheritance, the Moonstone, to the family estate in Yorkshire. He struggles with poor sleep after quitting tobacco and displays a mixture of sophisticated charm and stubbornness, eventually taking on the role of amateur investigator when the diamond vanishes.

Rachel is the young, wealthy heiress of the Verinder estate in Yorkshire. She is fiercely independent, accustomed to getting her own way, and highly protective of her privacy. After her newly inherited diamond goes missing, her behavior shifts dramatically, becoming cold and secretive toward those around her.

Gabriel serves as the loyal house-steward for the Verinder family, overseeing the domestic servants at their Yorkshire estate. He holds a deep affection for his employers and treats the young women in the house with fatherly care. He relies heavily on the novel Robinson Crusoe, consulting the book for guidance whenever he faces a difficult decision.

Godfrey is Rachel's cousin and a prominent barrister living in London. He is highly active in various charitable organizations and presents himself as a devout, morally upright Christian gentleman. He serves as a secondary suitor for Rachel's affections, providing a calm and respectable alternative to Franklin Blake.

Rosanna is a quiet, reclusive housemaid at the Verinder estate. She previously spent time in a reformatory for theft, a history known only to Lady Verinder and Gabriel Betteredge. She suffers from a physical deformity in her shoulder and often isolates herself from the other servants, acting strangely and defensively in the aftermath of the robbery.

Ezra Jennings works as an assistant to the local Yorkshire doctor, Mr. Candy. He is socially ostracized due to his unusual appearance and rumors of a past false accusation that ruined his reputation. He suffers from a painful, terminal illness and regularly consumes opium to manage his symptoms, giving him a unique perspective on medical matters.

Sergeant Cuff is a renowned police detective brought in from London to solve the mystery of the missing Moonstone. He possesses an eccentric demeanor but misses no small detail, immediately identifying wet paint on a doorframe as a key clue. His investigative methods cause friction with the upper-class members of the household.

Miss Clack is a highly religious and impoverished relative of the Verinder family who lives alone in London. She constantly attempts to convert her relatives to her strict evangelical views by hiding religious pamphlets around their homes. She idolizes Godfrey Ablewhite for his charitable work and judges anyone who does not share her faith.

Lady Verinder is the wealthy widow of Sir John Verinder and the matriarch of the Yorkshire estate. She is deeply suspicious of the diamond her estranged brother left for her daughter, fearing it is a malicious gift. She treats her household staff with benevolent respect, placing great trust in Gabriel Betteredge.

John Herncastle is Lady Verinder's estranged brother and a former British soldier. He steals the sacred Moonstone diamond from an Indian palace, taking the life of a guardian priest in the process. He bequeaths the cursed diamond to his niece, setting the primary conflict in motion.

Mr. Bruff serves as the long-time family lawyer for the Verinder family. He manages their wills, estates, and legal affairs with pragmatic efficiency. He relies on his extensive professional network to gather information and protect Rachel's financial interests.

Mr. Candy is the local physician in Yorkshire. He takes personal offense when Franklin Blake dismisses his medical advice regarding sleep aids. Shortly after the birthday party, he contracts a severe fever that permanently damages his memory.

An expert on Indian history and culture who attends the birthday dinner. He recognizes the disguised performers near the estate as high-ranking Brahmin priests and warns the family about the diamond's deep religious significance.

Penelope is Gabriel Betteredge's daughter and works as a maid in the Verinder household. She provides her father with helpful observations about the other servants and keeps a detailed journal that aids in reconstructing the timeline of the theft.

A London pawnbroker and moneylender. He becomes involved in the mystery after a valuable gemstone is deposited at his shop, leading to him being followed and briefly held captive by unknown men seeking information about the receipt.

The initial local police officer assigned to investigate the diamond's disappearance. He bumbles the early stages of the investigation by heavy-handedly interrogating the servants and offending the family before Sergeant Cuff replaces him.

A local young woman who lives at a fishing cottage near the Shivering Sands. She maintains a close friendship with Rosanna Spearman and holds onto a secret letter on Rosanna's behalf.

Three high-ranking Brahmin priests who travel from India to England to track down the stolen Moonstone. They use disguises and careful surveillance to locate the sacred artifact, remaining steadfast in their religious duty to return it to their homeland.

Rachel's deceased father and Lady Julia's late husband. He left his entire estate to his wife, an unusual legal move for the era that impacts how Rachel inherits her wealth and property.

Godfrey's father and Rachel's uncle. He briefly serves as Rachel's guardian in Brighton but angrily renounces the responsibility when she breaks off her engagement to his son.

Godfrey's mother and Rachel's aunt. She travels to Brighton to help settle Rachel into her new home before family tensions cause them to part ways.

Rachel's aunt who takes over as her guardian in London. She acts as a strict chaperone and complains about having to travel to Yorkshire for Ezra Jennings's experiment.

The owner of a local fishing cottage near the Yorkshire estate. She speaks with the police about Rosanna Spearman's movements and purchases on the day following the theft.

A young boy hired by the lawyer Mr. Bruff to keep watch on a London bank. He possesses sharp observational skills and tracks suspicious individuals through the city streets to an inn.