There are a number of works that attempt to situate a historical narrative to autism (Histoire de l'autisme by Hochmann is perhaps the most complete but Mitzi Waltz's Autism: A Social and Medical History is a good one in English). As a diagnosis, it was a term coined by Bleuler in 1913 as a subset of schizophrenia (then appropriated again by Kanner in 1943 for his research). However, some authors have noted that Itard's work with the Wild Boy of Aveyron constitutes an early discovery of autism in the early 19th century. Another is Peter the Wild Child (See Paul Collins *Not Even Wrong) Certainly Grinker's work (Unstrange Minds, as referenced by u/amneyer) reminds us of cultural variation concerning the defining of autism (especially between the Western world and the non-Western world). However, the difficulty of psychohistory (in this context) is the continuing change in how autism is defined (the current use of the notion of the spectrum derived from Lorna Wing's work in the 1970s). I would argue that is problematic to apply current psychological schema to historical figures based on the evidence left behind, mostly due to the subjectivity of the terminology (there is still not a consensus on how to diagnose autism among the global psycho-medical community).

Retroactive diagnoses of physical and psychological maladies are controversial even amongst physicians themselves - not least among historians of medicine, nearly all of whom reject the concept behind it.

There's a huge set of problems in ascribing disease and disorder pathologies to historical figures. In the first case, any information we have on historical figures is fragmentary, semantic, and often counter-intuitive to scientific thinking. No medical professional would render a diagnosis without direct observation of a patient - something unavailable to historians. Today, we might be inclined to view an individual, a series of actions, or a situation and ascribe a pathology to something that was entirely ordinary for that historical time and context. And that's not even considering that any evidence we do have is going to be coded in a particular historical context that needs to be read critically as a historical source; we can't take it as a bald scientific truth, which is what I often see with these kinds of "diagnoses."

It also privileges our own knowledge of disease over people's in the past. By that, I don't mean that one or another group "knows more" about medicine, but rather that people in different historical periods experience disease in different ways, and that can often affect how we judge and think about medical conditions.

To take one example, several years back when scientists mapping the human genome were making headlines, one researcher proposed that composer Frederic Chopin's mysterious death was likely caused by Alpha-1-antitrypsin deficiency, a genetic defect, based on an examination of his personal letters. One savvy historian of medicine pointed out that there have been major shifts in the theory of "what killed Chopin?" over the last century based on whatever medical knowledge predominated at the time, and all ostensibly garnered from the same source material. Since the late 19th century, doctors have retroactively diagnosed Chopin's major medical issue as tuberculosis (1899), psychasthenia (1899 and 1935), cyclothymic disposition (1920), tuberculosis psychoneurosis (1922, 1932), depressive or schizoid psychopathy (1948, 1950), allergic conditions (1961), valvular stenosis (1964), cystic fibrosis (1987), and major depressive disorder/bipolar disorder (2005).

None of that, of course, gives us any historical insight into how people in Chopin's time understood any of these diseases, and it's even anachronistic to use these terms because contemporary historical figures had no scientific, social, or cultural knowledge associated with them. In short, if you go looking in historical sources for something specific, you're going to find it.

In the case of historical figures being diagnosed with autism, most of the cases I've seen no only miss this vast forest for the trees, but are very thin merely on their clinical merit. Most are claims proposed by individuals with ulterior motives more interested in "claiming" a historical figure for their own objectives than any pretense for historical accuracy.

If you want a more intimate perspective on the difficulties of assigning medical and psychological diagnoses to historical figures, there's a chapter in Lytle and Davidson After the Fact: The Art of Historical Detection about John Brown's raid on Harper's Ferry and the problems with some ill-conceived attempts by psychohistorians to diagnose him with paranoid schizophrenia. It's very accessible, it's an entertaining read, and it does a great job of explaining the limits of historical evidence.