Joseph Bell was the real-life surgeon who inspired the character of Sherlock Holmes.
Bell was a Scottish surgeon and lecturer at the University of Edinburgh. Arthur Conan Doyle met him in 1877 while working as Bell’s outpatient clerk at the Edinburgh Royal Infirmary. Doyle was struck by Bell’s ability to diagnose patients and infer details about their lives from tiny observations before they had explained their symptoms.
That method became a foundation for Holmes’s famous powers of observation and deduction. Doyle later wrote to Bell that he owed him Sherlock Holmes, although Bell modestly suggested that Doyle himself was the true Holmes. Bell was not a detective prototype in every respect, and other figures, including forensic expert Henry Littlejohn, may also have influenced Doyle. Still, Joseph Bell is the canonical answer because Doyle explicitly acknowledged his importance.