Autistic kids and teens are way too common a device for me -
whether "idiot savant" or just "idiot". I don't want to blame
Dustin Hoffman but a lot of these subsequent portrayals,
including Haddon's apparently, are not based on knowledge or
understanding of autism conditions - "not any specific disorder",
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https://en.wikipedia.org/wiki/The_Curious_Incident_of_the_Dog_in_the_Night-Time>
If you want a character, especially a child, to be weird or
creepy or socially unperceptive or just not to behave like an
actual kid normally would in a horrific situation (scream and
run away, repeatedly, and demand food and a bathroom), here's
your licence. it's also an excuse for making a character
unbelievably smart.
Maybe I should blame Leonard Nimoy, or, specifically,
Gene Roddenberry. In the actual Star Trek TV series,
and some books, other characters usually discuss and
treat Spock the (Half) Vulcan's estrangement from
earth-human emotions as a disability. More thoughtful
treatments make it a conscious choice. An emotionally
expressive Vulcan is a lot harder to deal with.
According to Wikipedia, Sir Arthur Conan Doyle based
Sherlock Holmes on a teacher at medical school,
Dr Joseph Bell, but Bell saw Holmes as a version
of Doyle - at least I think that's the point, unless
he was trying to say that Doyle was more Holmes than
he was Watson (private general practising doctor with
a lot of free time in his patient appointment book).
So, those are actual people to look at.
Of course another way to have an oddball character
is to make them an alien, or an artificial intelligence,
or, as a relatively modern device, a supernatural being.
Well - "Lord, what fools these mortals be!" Not recent...