What real life person was sherlock holmes modeled after?

Sherlock Holmes was modeled after Sir Arthur Conan Doyle

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Sir Arthur Conan Doyle’s fictional detective with the knack for solving crimes through observation and reason was modeled after Dr. Joseph Bell, one of Conan Doyle’s medical school professors. Conan Doyle, born in Scotland in 1859, studied medicine at the University of Edinburgh and went on to work as a physician in England while writing fiction in his spare time. "A Study in Scarlet," his first novel featuring Sherlock Holmes, debuted in 1887. Conan Doyle eventually published a total of four novels and 56 short stories starring the London-based sleuth, whose keen observation skills were based in part on those of Joseph Bell.