From Wikipedia

A Study In Sherlock

Sherlock Holmes  is a fictional character of the late 19th and early 20th centuries who first appeared in publication in 1887. He was the creation of Scottish author and physician Sir Arthur Conan Doyle. A brilliant London-based "consulting detective", Holmes is famous for his intellectual prowess and is renowned for his skillful use of astute observation, deductive reasoning and forensic skills to solve difficult cases.

Conan Doyle wrote four novels and 56 short stories that feature Holmes. The first story, A Study in Scarlet, appeared in Beeton's Christmas Annual in 1887 and the second, The Sign of the Four, in Lippincott's Monthly Magazine in 1890. The character grew tremendously in popularity with the beginning of the first series of short stories in The Strand Magazine in 1891; further series of short stories and two serialised novels appeared until 1927. The stories cover a period from around 1880 up to 1907, with a final case in 1914.

All but four stories are narrated by Holmes' friend and biographer, Dr. John H. Watson; two are narrated by Holmes himself ("The Blanched Soldier" and "The Lion's Mane") and two others are written in the third person ("The Mazarin Stone" and "His Last Bow"). In two stories ("The Musgrave Ritual" and "The Gloria Scott"), Holmes tells Watson the main story from his memories, while Watson becomes the narrator of the frame story.

Conan Doyle said that the character of Holmes was inspired by Dr. Joseph Bell, for whom Doyle had worked as a clerk at the Edinburgh Royal Infirmary. Like Holmes, Bell was noted for drawing large conclusions from the smallest observations.