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.

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.

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.