Conan Doyle wrote later, “It was as though in the guise and dress of a man I had caught a sudden glimpse of something subhuman—of something so outside my own range of thought that I was powerless against it” (The Stark Munro Letters, p. 271). He was also powerless to explain it. Whenever he depicts some descent into the abyss of vice, it is inevitably without any insight into how a soul makes such a journey: It is always taken as merely a fact of existence.

It was a few years later, in 1886, after he had set up a mildly profitable medical practice of his own, that Conan Doyle first turned to the idea of a detective novel. In addition to his Edinburgh models, Sherlock Holmes had literary sources, too. Conan Doyle had read and admired the detective stories of Edgar Allan Poe, the creator of the genre, as well as the detective novels of Emile Gaboriau, whose Monsieur Lecoq solved some baffling crimes. Holmes’s methods are similar to those of Poe’s C. Au guste Dupin, and the stories have a structure reminiscent of Gaboriau’s work, but his personality owes nothing to either of those Parisian detectives. And ultimately it is his personality that makes Holmes so compelling.

Just what is it about Sherlock Holmes that has captivated people for so long? It’s easy to see some of the reasons for his popularity. His intelligence, his self-assurance, his mastery of every situation, and his unerring judgment are all enormously appealing. We are also attracted by Holmes’s sense of humor. From the very first Holmes not only sprinkles the stories with his dry retorts and ironic asides, he also laughs, chuckles, smiles, and jokes throughout. This quality goes a long way toward humanizing him, making it easier to feel affection for a character whose abilities could well make him seem more machine than human.

His eccentricities add to his appeal. An unwritten rule says that every commentator must mention the tobacco he keeps in the toe end of his Persian slipper, the cigars he keeps in a coal-shuttle, and the unanswered correspondence he transfixes by a jack-knife into the very center of his wooden mantelpiece. But his odd qualities extend further than these surface details. They are really only shallow tricks that add some local color, perhaps, to his characterization, but reveal little about his character. More revealing of just how truly eccentric he is are the passions central to his mind and the lengths he is willing to go in their service.

Devoting his life to fighting crime, for instance, is surely unusual. With his skills and connections, one would think he could have had his choice of careers. What sort of person dedicates himself to catching people who commit crimes? We don’t need a psychiatrist’s shingle to conclude that someone who feels this need must have suffered some sort of injustice as a child. As we can never know what this sad event was, we can only speculate, and many have. Whatever it was, it has made Holmes a moralist. It is not the law that he upholds, but his own conception of justice. Several times he substitutes this conception for the letter of British law by letting someone go who is guilty of a crime. Several other times he violates the law himself in order to bring about some higher justice. Those are some of the things we admire about him. Because we always agree with his judgment in those instances, his willingness to become the final arbiter of justice makes him heroic.

Holmes is of course a gentleman, with all the notions of class in nineteenth-century England that the word implies. Yet he does things no gentleman would dream of doing. On one occasion he disguises himself as a beggar, on another as an opium addict, and, most improbably of all, on another as an old woman. Since these disguises help him get to the truth, we think of them, if we think of them at all, as merely techniques, albeit clever and entertaining ones, for solving crimes. But respectable men in London in the 1890s would be aghast at seeing a fellow they knew sauntering forth in a frock and a wig, or holed up in an opium den.