Who "dribbled a lot and wasn’t allowed anything sharp" in "Good Omens"?

Question

While reading Good Omens by Terry Pratchett & Neil Gaiman, I stumbled across the following quote, in which Aziraphale’s calculations are described:

But these other calculations were of a kind no computer could ever do. Sometimes he would scribble something on a sheet of paper by his side. It was covered in symbols which only eight other people in the world would have been able to comprehend; two of them had won Nobel prizes, and one of the other five dribbled a lot and wasn’t allowed anything sharp because of what he might do with it.

Who is that last person they’re referring to? I looked it up, but found no explanation. I feel like I’m missing a pop-culture reference.

Edit: By the way, my edition is the GOLLANCZ 2013 and the quote is on page 168.

Edit 2: I'm so glad that a simple question like this brought me closer to such brilliant answers.

Answer 1

While I think Gareth's answer is what was intended, it's also possible that they were referring to an Idiot Savant situation, which is the idea that someone with mental problems is sometimes brilliant in a particular area. Today, this is often associated with autism, such as with Rain Man, but is also sometimes tied in with schizophrenia as in A Beautiful Mind, or bipolar disorder where an artist might create their greatest works during their fits of mania or depression.

Answer 2

It’s not an allusion to any particular person, but to a trope that is common in the supernatural horror genre, namely that some texts are so disturbing that people can go insane just by reading them. The implication is that this is what happened to the person described in the quoted extract, when he read a book written in the symbols employed by Aziraphale.

An early example of this trope is the short stories of Robert W. Chambers, in which the play The King in Yellow has this effect on its readers:

During my convalescence I had bought and read for the first time, The King in Yellow. I remember after finishing the first act that it occurred to me that I had better stop. I started up and flung the book into the fireplace; the volume struck the barred grate and fell open on the hearth in the firelight. If I had not caught a glimpse of the opening words in the second act I should never have finished it, but as I stooped to pick it up, my eyes became riveted to the open page, and with a cry of terror, or perhaps it was of joy so poignant that I suffered in every nerve, I snatched the thing out of the coals and crept shaking to my bedroom, where I read it and reread it, and wept and laughed and trembled with a horror which at times assails me yet.

_{Robert W. Chambers (1895). ‘The Repairer of Reputations’. In The King in Yellow. Project Gutenberg.}

The trope is best known through the works of H. P. Lovecraft, whose story ‘The Hound’ (1924) introduced the “forbidden Necronomicon of the mad Arab Abdul Alhazred”, which has similar effects on its readers.

(Note that despite having written this, I think Sean Duggan’s answer is the better one—the text in Good Omens is closer to a stereotypical description of an idiot savant than it is to that of a madman.)

Answer 3

No one important, a random mental patient.

The key isn't that there is a person who are currently able to comprehend his work, its that these are the only people who would have been able to comprehend them (were they given the opportunity). Therefore the person is already broken. In either case, this is just an interesting fact and the unnamed person is not important to the story.

My understanding is that in order to understand the writings (either of the divine, Aziraphale himself, of some combination thereof), you have to either be incredibly unimaginably creative, or absolutely broken. Considering the line

But these other calculations were of a kind no computer could ever do.

to me suggests it isn't an issue of processing power (and thus raw intelligence), but un-intuitive thought processes. The kind that lead to either revolutionary ideas, or complete madness. This would be an inversion of the Lovecraftian trope where rather than understanding bringing madness, where in this case only the mad are capable of understanding. (Though Lovecraft I believe played with both, the trope generally goes one way)

Presumably, the other 4-5 people are very nearly at either of the ends, or indeed both. Possibly they may be otherwise exceptionally peculiar but in a way not worth mentioning.