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.

An American criminal whose pursuit of a woman from his past brings violence to a quiet Norfolk farm in The Adventure of the Dancing Men. His use of a coded message system based on stick figures dancing - the dancing men of the title - gives Holmes one of his most celebrated cryptographic challenges. Dangerous and entirely without scruple about pursuing what he considers his by prior claim.

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.

The last scion of an ancient Surrey family whose violent temper makes him one of the more physically imposing figures in the canon. A trained physician who spent years in India, he returned with exotic animals collected during his service abroad. The peculiar circumstances of his household at Stoke Moran are what Holmes is asked to investigate in The Adventure of the Speckled Band.

A highly intelligent and audacious criminal of aristocratic bearing - described by Holmes as occupying the fourth smartest position in London. A man of good family and considerable gifts entirely devoted to crime, whose particular ingenuity in the Red-Headed League affair gives that case one of the canon's more enjoyable solutions.

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.

A Norfolk squire of old family who comes to Holmes with a curious problem - a series of stick figure drawings appearing on his property that have thrown his American wife into a state of terror she refuses to explain. Straightforward, decent, and entirely out of his depth in the situation his wife's past has brought to his door. Appears in The Adventure of the Dancing Men only.

A young and promising Scotland Yard inspector whom Holmes regards as one of the best of the official force. Appears across several cases in The Return of Sherlock Holmes, where he frequently brings difficult cases to Holmes while remaining open to methods that his more senior colleagues would dismiss. Represents a younger, more adaptable face of official detection.

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.

An American opera singer and adventuress who appears in a single story, A Scandal in Bohemia, but earns a permanent place in the canon. Referred to thereafter simply as The Woman. Her prominence in adaptation far exceeds her actual canonical presence, but her impact on Holmes's characterisation is genuine and lasting.

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.

Sherlock Holmes's elder brother, possessed of even greater powers of observation and deduction but entirely lacking his sibling's energy or inclination to act on them. A founding member of the Diogenes Club and a figure of considerable, deliberately vague importance within the British government - Holmes suggests at one point that Mycroft occasionally is the British government. Appears rarely but significantly.

A London pawnbroker whose extraordinary red hair brings him to Holmes's attention in The Red-Headed League. Slow, stout, and rather out of his depth, he presents one of the more peculiar cases in the canon. Appears in one story only.

A governess who engages Holmes in The Adventure of the Copper Beeches, one of the canon's more unsettling cases. Bright, practical, and possessed of more courage than her situation warrants, she impresses Holmes sufficiently that Watson notes his unusual regard for her. Appears in one story only but is among the more memorable of the canon's single-appearance clients.