Army surgeon invalided home from Afghanistan who becomes Sherlock Holmes's companion, lodger, and chronicler. Steady, decent, and possessed of considerable courage, he serves as both the practical counterweight to Holmes's eccentricity and the reader's point of entry into a world that would otherwise be entirely alien. Narrator of the overwhelming majority of the canonical stories.

The world's only consulting detective, operating from 221B Baker Street, London. Possessed of extraordinary powers of observation and deductive reasoning, he applies a rigorous scientific method to criminal investigation while remaining largely indifferent to conventional social expectations. Capable of brilliant warmth and profound coldness in equal measure, his partnership with Dr Watson is the central relationship of the canon.

Former Colonel of the First Bangalore Pioneers and big game hunter, described by Holmes as the second most dangerous man in London after Moriarty. Chief of staff to Moriarty's criminal organisation. Appears in The Adventure of the Empty House.

A naturalist and amateur entomologist living on the edge of the great Grimpen Mire, near the Baskerville estate in The Hound of the Baskervilles. Affable, well-read, and disarmingly enthusiastic about the rare butterflies of Dartmoor, he and his sister Beryl quickly take an interest in the new heir to Baskerville Hall.

A physically powerful American cab driver who comes to Holmes's attention during the investigation of a murder in Lauriston Gardens. His history in the Utah Territory and his connection to the victims of the case only becomes clear as Holmes pursues his inquiries. Appears in A Study in Scarlet only.

A one-legged former soldier whose history in India and subsequent years of imprisonment connect him to the mystery at the heart of The Sign of Four. His full story, told in the novel's final chapter, reframes much of what has preceded it. Appears in The Sign of Four only.

A former Professor of Mathematics turned criminal mastermind, described by Holmes as the Napoleon of Crime - the organising intelligence behind much of London's serious criminality. Appears directly in only a handful of stories but casts a shadow across the later canon.

An American whose appearance at Birlstone Manor is the inciting incident of the murder investigation at the centre of The Valley of Fear. His connection to John Douglas and to the events described in Part 2 of the novel becomes clear as Holmes's investigation progresses. Appears in The Valley of Fear only.

An Andaman Islander who became the devoted companion of Jonathan Small, accompanying him to England. His presence aboard the Aurora during the Thames chase is one of the more startling moments in the novel. Appears in The Sign of Four only.

The woman presented as the sister of the naturalist Stapleton at Merripit House on Dartmoor. Her nationality, the particular nature of her position in the household, and the genuinely sympathetic warmth she shows toward Sir Henry Baskerville are at the heart of the difficult and slowly unfolded solution of the Baskerville case. Appears in The Hound of the Baskervilles only.

A country doctor and man of science who brings the Baskerville case to Holmes, having witnessed the death of Sir Charles Baskerville and found evidence that defies rational explanation. Scholarly, nervous, and genuinely frightened, he is the reader's introduction to the Dartmoor world of The Hound of the Baskervilles and one of its more sympathetically drawn supporting figures.

Scotland Yard's most prominent inspector in the canon and Holmes's most frequent professional contact within the official police. Tenacious and not without competence, but habitually out of his depth on the cases that matter most, he represents the institutional approach to detection that Holmes consistently outpaces. His relationship with Holmes evolves from grudging tolerance to genuine respect across the canon.

The owner of Birlstone Manor whose apparent murder brings Holmes and Watson to Sussex at the opening of The Valley of Fear. A man of considerable physical presence and personal courage whose history proves considerably more complex than it initially appears. Appears in The Valley of Fear only.

Introduced in The Sign of Four as a client of Holmes and Watson. Quietly courageous and clear-headed in difficult circumstances, she is described as small, fair, and refined.

Landlady of 221B Baker Street and the domestic anchor of Holmes's unconventional household. Tolerates her tenant's erratic hours, dangerous visitors, and destructive experiments with remarkable equanimity. More resilient and resourceful than her role suggests, she is a constant presence across the canon without ever being its focus.

The Canadian-raised heir to the Baskerville estate on Dartmoor, drawn back to England by the death of his uncle Sir Charles and the apparent threat of a family curse. Direct, practical, and considerably braver than his situation might warrant, he is the client and central concern of The Hound of the Baskervilles - the most celebrated case in the canon.