Sherlock Holmes () is a fictional private detective created by British author Sir Arthur Conan Doyle. Referring to himself as a "consulting detective" in the stories, Holmes is known for his proficiency with observation, forensic science, and logical reasoning that borders on the fantastic, which he employs when investigating cases for a wide variety of clients, including Scotland Yard. First appearing in print in 1887 (in A Study in Scarlet), the character's popularity became widespread with the first series of short stories in The Strand Magazine, beginning with "A Scandal in Bohemia" in 1891; additional tales appeared from then until 1927, eventually totalling four novels and 56 short stories. All but one are set in the Victorian or Edwardian eras, between about 1880 and 1914.

Edgar Allan Poe's C. Auguste Dupin is generally acknowledged as the first detective in fiction and served as the prototype for many that were created later, including Holmes. Conan Doyle once wrote, "Each [of Poe's detective stories] is a root from which a whole literature has developed... Where was the detective story until Poe breathed the breath of life into it?" Similarly, the stories of Emile Gaboriau's Monsieur Lecoq were extremely popular at the time Conan Doyle began writing Holmes, and Holmes' speech and behaviour sometimes follow that of Lecoq. Both Dupin and Lecoq are referenced at the beginning of A Study in Scarlet.  Conan Doyle repeatedly said that Holmes was inspired by the real-life figure of Joseph Bell, a surgeon at the Royal Infirmary of Edinburgh, whom Doyle met in 1877 and had worked for as a clerk. Like Holmes, Bell was noted for drawing broad conclusions from minute observations. However, he later wrote to Doyle: "You are yourself Sherlock Holmes and well you know it". Sir Henry Littlejohn, Chair of Medical Jurisprudence at the University of Edinburgh Medical School, is also cited as an inspiration for Holmes. Littlejohn, who was also Police Surgeon and Medical Officer of Health in Edinburgh, provided Doyle with a link between medical investigation and the detection of crime.  Other inspirations have been considered. One is thought to be Francis "Tanky" Smith, a policeman and master of disguise who went on to become Leicester's first private detective. Another might be Maximilien Heller, by French author Henry Cauvain. It is not known if Conan Doyle read Maximilien Heller, but in this 1871 novel (sixteen years before the first adventure of Sherlock Holmes), Henry Cauvain imagined a depressed, anti-social, polymath, cat-loving, and opium-smoking Paris-based detective.

When was Joseph born?