Nevertheless, the iconic fictional detective would not have existed but for Edgar A. Poe.
In 1841, Poe published "The Murders in the Rue Morgue," widely considered the first modern detective story. Poe's well-known recurring fictional "detective" character is C. August Dupin — a socially-awkward yet highly intelligent gentleman who relies on a combination of logic and imagination. With him, as always, is his nameless friend, who serves as both bumbling sidekick and the first-person narrator of Dupin's exploits.
Doyle, you might recall, introduced his fictional detective, Sherlock Holmes, as a socially-awkward yet highly intelligent gentleman as well, and all of his stories include his assistant Watson, who serves as both bumbling sidekick and the first-person narrator of Holmes's exploits. In other words, Poe created the model of fictional detectives which Doyle popularized (I won't say "perfected," as I'm not too familiar with his works).
Of course, Doyle does pay an homage of sorts to his source of inspiration. In the aforementioned A Study in Scarlet, the Watson character attempts to pay Holmes a "compliment" in chapter 2:
"It is simple enough as you explain it," I said, smiling. "You remind me of Edgar Allan Poe's Dupin. I had no idea that such individuals did exist outside of stories."
Sherlock Holmes rose and lit his pipe. "No doubt you think that you are complimenting me in comparing me to Dupin," he observed. "Now, in my opinion, Dupin was a very inferior fellow... He had some analytical genius, no doubt; but he was by no means such a phenomenon as Poe appeared to imagine."
Holmes's snide remarks aside, it is now generally understood that Doyle's work owes more than a little to Poe's. Incidentally, there are detractors who suggest that Poe was not the first to write a mystery story. This is true enough, yet Poe's model allows the mystery to be solved by a specific individual who makes it his role to deduce the answer. At the time "The Murders in the Rue Morgue" was published, there was not a single professional detective anywhere in the country — in fact, the word "detective" was not yet coined. Poe referred to the process Dupin uses not as "detection" but "ratiocination" — and it has part of the word "imagination" right there in it.
Oddly, Poe found writing these stories a little boring. As he wrote, "where is the ingenuity in unraveling a web which you yourself... have woven for the express purpose of unraveling?" Good question, coming from a guy who liked to play hoaxes on his audience. In fact, Poe even parodied the very genre he invented. The little-known tale "Thou Art the Man!" is Poe's burlesque of the modern detective story, before the genre was identified beyond "something in a new key."
Happy birthday to Sir Arthur Conan Doyle, whose Sherlock Holmes character is sure to entertain for generations to come.