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.

Question: What other inspirations have been considered?
Self-contained rewrite: What other inspirations for Sherlock Holmes have been considered besides C. Auguste Dupin and Émile Gaboriau?