To truly wrap your head around BBC’s Sherlock, one must go to the source material written by Sir Arthur Conan Doyle. Mark Gatiss and Steven Moffat are such Doyle fanboys (they’ve been reading the books since they were in short pants), it’s often astonishing to find all of the little nods the writers slip into the individual scripts.

Born in 1859 in Edinburgh, Doyle was enrolled in a prep school by age nine, and being away at boarding school meant a treasure trove of letters home to his mother, Mary, whom he referred to as “the Mam.” These letters, finally opened to the public in 1997 by the Doyle family, offer extraordinary insight into the complicated man who’s as fascinating as the detective he created. Doyle studied to become a medical doctor, and at the University of Edinburgh Medical School he met the larger-than-life Joseph Bell, a professor who had a huge impact on Doyle’s life. At 39 years old, Bell was still rather young, but he was, according to Doyle biographer Russell Miller, “already a legend among medical students as a master of observation, logic, and deduction, possessing almost clairvoyant powers of diagnosis.” Bell taught the students how to diagnose a patient without asking them a single question, instead simply observing the patient and concluding from those observations what might be wrong. He believed that while the patient could provide information that was invisible to the doctor, there was a wealth of information available if one only observed properly. He used a trick in class to emphasize the importance of noticing small details: he passed around a container of horrible-tasting liquid, asking the students to stick their fingers in it and taste it. In the name of fairness, he did it first, which forced each student to do it after him. Only after the container made its way throughout the classroom, much to the discomfort of each student’s tongue, did he confess that he had stuck his index finger into the container but sucked on his middle finger. If they’d only paid close attention, they would have saved their tastebuds the horrible experience they’d just undergone.

Bell’s methods stuck with Doyle, and after he graduated he opened his own practice in Southsea. He began publishing fiction on the side, and in 1885 he married Louise Hawkins (whom he referred to as Touie). Two years later, Touie wrote to Doyle’s sister Lottie, “Arthur has written another book, a little novel about 200 pages long, called A Study in Scarlet. It went off last night.”

Doyle had long been a fan of the work of Émile Gaboriau, known as a pioneer of modern detective fiction, and Edgar Allan Poe’s Chevalier Dupin, and had longed to create a detective character of his own. He wrote in his memoir, “I thought of my old teacher Joe Bell, of his eagle face, of his curious ways, of his eerie trick of spotting details. If he were a detective he would surely reduce this fascinating but unorganised business to something nearer to an exact science …” It was in this characterization of Joseph Bell that Doyle hit upon what would set his detective fiction apart from everything that had come before it: Sherlock Holmes would, according to Miller, “solve his cases by pure deduction and not, as was commonplace in popular detective fiction, because of an absurdly convenient coincidence which, [Doyle] said, ‘struck me as not a fair way of playing the game.’”

The first Sherlock Holmes novel was not an overnight success, even though it was a brilliant introduction to the character who was, as Orson Welles once put it, “the world’s most famous man who never was.” It was published in Beeton’s Christmas Annual in 1887 for a one-time author fee of £25, with no ongoing royalties. (One can only imagine the income that Doyle and his heirs have lost in the years since its publication.) Despite the tepid public reaction to A Study in Scarlet, Doyle published the second Holmes novel, The Sign of Four, in 1889, and in 1891 Holmes short stories began appearing in the Strand. Excellent reviews for The Sign of Four led to an increased readership, and the new enthusiasm and public demand for more stories led to Doyle closing his practice to become a full-time writer; he was making more money through the stories than he made in his practice. The paltry payment he’d been given for A Study in Scarlet is less difficult to accept when one realizes that by the turn of the century Doyle was the highest-paid author in the world.

Critics praised the ingenious storylines: Doyle could write about Mormonism, then switch to a story involving the Indian Mutiny and an evil pygmy dwarf who picks off his victims with a blowpipe. What audiences winced at, however, was the revelation in The Sign of Four that Holmes was a cocaine addict. At the time, cocaine was not perceived as being as nefarious as it is now; in fact, it was regularly used in hospitals as an anesthetic (along with heroin), and one could obtain it with little to no hassle. But still, according to Miller, “Some readers were appalled that a man of Sherlock Holmes’s intellect and strength of character would inject himself with drugs, but Conan Doyle always wanted to distance his detective from the plodding image of a policeman: languid, bohemian, aesthetic, eccentric, Holmes viewed the science of criminal investigation as an art form and, as an artist, why should he not enjoy the pleasures of the needle?”

Doyle wrote each short story in under a week with almost no research (which accounts for the vast number of glaring inconsistencies between them). “A Scandal in Bohemia,” where Holmes is faced with a woman as brilliant as he is and must try to stop a royal scandal, was a smash hit upon publication. Doyle’s editor, Herbert Greenhough Smith, described what it was like receiving the manuscripts for the first time: “Here, to an editor jaded with wading through reams of impossible stuff, comes a gift from Heaven, a godsend in the shape of the story that brought a gleam of happiness into the despairing life of this weary editor.”

Doyle suggested to the Strand that they use Walter Paget, who worked with several magazines at the time, for the Holmes illustrations, but the art director couldn’t recall his first name, so he simply sent the request to “Mr. Paget.” It fell into the hands of Walter’s brother Sidney, who took the job. Illustrating the story “Silver Blaze” (which ultimately became the first story in the second collection, The Memoirs of Sherlock Holmes), Paget drew the detective in a deerstalker hat and a long cape, which have now become synonymous with Sherlock Holmes (despite the fact that Doyle never mentions either accoutrement in the stories).

By 1892, people were lining up at the newsagents waiting for a new story to come out, and Doyle was baffled and annoyed. He had wanted Sherlock Holmes to be a one-off character, not one that he would have to continue writing about for the rest of his life. A Study in Scarlet was written over a three-week period when Doyle was 27 years old, and by the time he was in his early 30s, he wanted to be finished with the great detective so he could focus on his science fiction and historical fiction. In a letter to his mother, he revealed that he’d decided to kill the character, and despite her pleading with him not to, he began working on that final story. In a letter in 1893 he wrote to her, “I am in the middle of the last Holmes Story, after which the gentleman vanishes, never never to reappear. I am weary of his name.”

And so, later that year, he killed off his greatest character in a fight to the death with the evil Professor Moriarty (a mathematician, a career choice inspired by Doyle having detested mathematics as a boy), as both of them tumbled over the great Reichenbach Falls in “The Final Problem.” The story was published just before Christmas, and readers were devastated and went into mourning, some young men going so far as to wear black crepe mourning bands on their hats or arms. For Doyle’s part, he simply wrote in his journal, “Killed Holmes.”

The detective was dead, and Doyle tried to move on with his life and his writing. His father, who had been a severe alcoholic and was institutionalized at the time, died, and then Doyle’s wife, Touie, contracted tuberculosis. Doyle began traveling, first becoming a war correspondent in Egypt, then in South Africa during the Boer War. Upon his return, he published some historical novels and continued to take care of his wife as she battled TB.

In 1897, he met and fell in love with another woman, Jean Leckie, but both vowed that despite their love, they would not act upon it until Touie had died. (Neither one of them could have foreseen that Touie was going to hang on for another nine years.) Leckie became a regular visitor at the home and got to know Doyle’s two children, Mary and Kingsley. Doyle’s letters to his mother during this long period express his passion for Jean, his love and devotion to Touie, his frustration at the situation, and even some regret. It’s unclear if Touie knew about Doyle and Jean’s true feelings for each other, though it’s likely she did.

In 1899, actor William Gillette portrayed Sherlock Holmes for the first time on the London stage. The play, written by Gillette with the approval and aid of Doyle, was an overnight success. Doyle had been hesitant at first, and turned down previous suggestions of putting Holmes onstage. “I am well convinced,” he wrote in the early 1890s, “that Holmes is not fitted for dramatic representation. His reasonings and deductions (which are the whole point of the character) would become an intolerable bore upon the stage.” The very first time Doyle met Gillette, however, Gillette stepped off the train in a cape and deerstalker, and began to deduce that Arthur Conan Doyle was indeed the famous writer of the Sherlock Holmes stories. Doyle was instantly charmed, and Gillette looked exactly the way Doyle had always pictured Holmes in his head.

Unfortunately for Doyle, the success of the play led to a renewed clarion call for new Sherlock Holmes stories. Doyle had long been fascinated by the supernatural and had an idea for a story about a terrifying hound on the moors. By reshaping the idea into a Sherlock Holmes novel (but, for the most part, actually removing Holmes from the action and having Watson do the detective work), he created a sensation when he published The Hound of the Baskervilles, about an heir to the Baskerville mansion and the family legend of a hound that kills members of the family. The plot takes place in 1889, before Holmes had “died.” The public was overjoyed that Holmes had returned, and Doyle decided he had to bring the detective back. Doyle was knighted, and a year later Sherlock returned to the land of the living in “The Adventure of the Empty House,” dressing up as an old bookseller and scaring his dear friend Watson into a dead faint when he revealed himself to be Watson’s long-dead friend.

One thing that dogged Doyle was the fact that the public seemed to think that he was Sherlock Holmes. When he showed up to readings he noted that audiences looked let down when he didn’t look like Holmes at all. He wrote angrily in one of his letters, “I learned afterwards that they expected to see in me a cadaverous-looking person with marks of cocaine injections all over him.” And yet, in 1906, Doyle was called in on a particularly difficult case for Scotland Yard, where a young man, George Edalji, had been charged with killing cows in his neighborhood. Doyle excitedly accepted the task, and successfully proved that Edalji did not, in fact, kill the cows, and that he had been set up and the case was more likely racism at work.

Later that year, Touie succumbed to tuberculosis. Despite having loved Leckie for as long as he had, Doyle was still devastated when his beloved wife died; the fact that she lived for 13 years after her diagnosis is a testament to how well he had taken care of her. However, upon his marriage to Leckie in 1907, Doyle immediately shipped both of his children off to boarding school, and surviving letters from his daughter, Mary, to his son, Kingsley, suggest that Doyle was treating them heartlessly as he moved on with Leckie, devoting himself to his wife and not even letting the children come home for holidays. Between 1909 and 1912, Doyle and Leckie had three more children, which pushed Mary and Kingsley even further out of the picture.

In 1912, Doyle published The Lost World, his most famous work outside the Holmes canon, and the reviews were very positive. Doyle was still writing Holmes stories at the same time — seven stories written between 1908 and 1917 comprise his fourth short-story collection, and The Valley of Fear, the fourth and final Holmes novel, was serialized from 1914 to 1915. But he was keen to write material outside of detective fiction.

When the First World War broke out in 1914, Doyle formed a volunteer force and was a tireless fundraiser for the soldiers, and his writing at the time reflects this involvement in the war effort. When his son Kingsley died of influenza a mere two weeks before the Armistice that ended the war, Doyle was beside himself.

During the war, Doyle became involved with spiritualism, and he and Leckie toured the world spreading the word of this cult. They held regular séances in their house, and Doyle sincerely thought he was bringing comfort to people who had lost loved ones in the war by encouraging the bereaved to contact the spirit world. Some people thought the Doyles were frauds, others believed they were just misled, and still others believed wholeheartedly in what they were doing. On one particular trip to the U.S., Doyle met up with Harry Houdini, who challenged him to make him a believer in spiritualism, claiming that spiritualists are simply using magic tricks. While Doyle was unable to convince him, the two men remained friends.

However, many other prominent figures in letters were starting to distance themselves from the great writer, believing that his devotion to spiritualism hinted that he had lost his mind. T.S. Eliot referred to Doyle’s “mental decay,” and P.G. Wodehouse suggested that Doyle had “simply fallen victim to hubris.”

Just before the end of the war, two little girls from Cottingley in northern England took photographs of fairies they had seen in the woods, with the little creatures dancing in trees and sitting on the girls’ hands. Despite the fact that the fairies were cut out from a popular children’s book, which should have tipped off most people, and stuck to the trees with hatpins, the public fell for the ruse. Doyle was called up to take a look at the photographs, and he declared them authentic in the Strand in 1920 and 1921; they formed the basis for his book The Coming of the Fairies in 1922. It wasn’t until 1985 — 55 years after Doyle’s death — that one of the girls finally admitted publicly that the photographs had been faked. She said that it was Doyle’s involvement that forced the girls to maintain their fiction, because she didn’t want to embarrass him.

Doyle devoted most of the rest of his life to touring the U.S., Australia, Canada, and South Africa to promote spiritualism, publishing books on the subject. He continued to write prolifically outside of the Holmes canon — in all he wrote 23 novels, almost 180 short stories, 17 books of non-fiction, and seven stage plays, including one libretto with J.M. Barrie — and his final collection of Sherlock Holmes stories was published in 1927.

Sir Arthur Conan Doyle died in July 1930 at the age of 71, and within 24 hours his family members reported having received messages from him from the other side. He “appeared” at his own funeral dressed in his evening clothes (according to a medium that was present) and his wife insisted that she received messages from him until her death in 1940.

Regardless of what anyone thinks of his beliefs later in life, and much to the chagrin of the author beyond the grave, Doyle will always be remembered for Sherlock Holmes, the detective who taught the world not just to look, but to observe.