While I am well aware most people know what and who Sherlock Holmes is, let me be autistic here, dammit. But BECAUSE most people already know about him, I won't go into major detail. If you are looking for major detail, here's the Wikipedia page on Sherlock Holmes for your reading pleasure. This page will also be...incredibly casual. I'm not rewriting a Wiki page here.
Sherlock Holmes as a series began in 1887 with one of the most iconic Holmes stories, A Study in Scarlet. From there, further stories were published in The Strand Magazine. Eventually, the stories were published formally, in four novels and fifty-six short stories. These stories have been printed and re-printed dozens of times in numerous collections over the years.
Holmes was not the first fictional detective by any means. Poe's C. Auguste Dupin and Gaboriau's Monsieur Lecoq were clear influences on Doyle as he wrote. But, as time has shown, Holmes managed to be arguably the most popular fictional detective ever put to written word. In fact, the character holds the distinction of a Guinness World Record for being the most portrayed human literary character ever made. Early Holmes fans were arguably the prototype for modern fandom. But, as many of us know, Doyle fucking hated his own character despite the sucess.
Enough talk about the books themselves, let's get into how I feel about Holmes as a character. Because that's why people make shrine pages, isn't it?
Sherlock Holmes as a character is...well, he's a doozy. Every adapation writes him a little differently, but a lot of his core personality traits stay in tact. He's aggressively blunt, oftentimes calling people out for little things to their face simply because he can, not to mention the fact that most Holmeses (is that the plural?) have a massive "smartest guy in the room" complex. To be fair, 9-times-out-of-10 he is the smartest guy in the room, but you know what I mean.
A part of this is the fact that Holmes just...makes conclusions based on very little evidence, and by virtue of the sandbox of fiction, he's almost always correct. He can decide everything about a singular person just based on the way they dress, hold themselves, etc. This of course lead to what is arguably the most well-quoted line from Holmes: "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."
Holmes is also often characterized by his drug abuse. The way I often read that is that he is self-medicating, as yes, I am one of those people who staunchly headcanon Sherlock to be autistic. He even says it himself in one of the stories--I forget which one exactly--that he does drugs when he's understimulated. If that's not a neurodivergent self-medicating, I don't know what is.
Another thing many versions like to include is his musicial talents, specifically with the violin. This is another thing I like to rope into my autistic-Holmes headcanon, as I like to imagine that the violin is how he stims.
I think one of my favorite random things about Holmes is that he, straight up, does not know things a normal man should. This is referenced at least once in BBC Sherlock, of all things, but most adaptations ignore it. In his first appearance, he tells Watson he doesn't know the Earth goes around the Sun because he doesn't think it's important knowledge. Like, thanks Holmes, you may be a great detective, but how is your brain so full of other things you can't hold onto a simple astronomy fact?