Conversation so far:
Who was the inspiration for Sherlock Holmes?
Edgar Allan Poe's C. Auguste Dupin is generally acknowledged as the first detective in fiction and served as the prototype for many later characters, including Sherlock Holmes.
How did Edgar Allen Poe inspire Sherlock Holmes?
Conan Doyle once wrote, Each [of Edgar Allan Poe's detective stories] is a root from which a whole literature has developed.“
Are there any other interesting aspects about the Sherlock Holmes article?
Similarly, the stories of Émile Gaboriau's Monsieur Lecoq were extremely popular at the time Conan Doyle began writing Sherlock Holmes, and Holmes' speech and behaviour sometimes follow that of Lecoq.
What other inspirations for Sherlock Holmes have been considered besides C. Auguste Dupin and Émile Gaboriau?
Conan Doyle repeatedly said that Sherlock Holmes was inspired by the real-life figure of Joseph Bell.
Who was Joseph Bell?
Joseph Bell was a surgeon at the Royal Infirmary of Edinburgh, whom Conan Doyle met in 1877 and had worked for as a clerk.
Is there anything else you can tell me about Joseph Bell besides being a surgeon?
Like Sherlock Holmes, Joseph Bell was noted for drawing broad conclusions from minute observations.
Did Sherlock Holmes have any other inspirations besides Jordan Bell, Auguste Dupin and Émile Gaboriau??
Sir Henry Littlejohn Chair of Medical Jurisprudence at the University of Edinburgh Medical School is also cited as an inspiration for Sherlock Holmes.

Question: How did LittleJohn inspire Holmes?
Self-contained rewrite: How did Sir Henry Littlejohn inspire Sherlock Holmes?