From The Encyclopedia of Human Thermodynamics, Human Chemistry, and Human Physics:
Last person to know everything
In genius studies, the last person to know everything or the “last man to know everything” is a title or epitaph that has been attributed to a number of individuals over the years. The following page gives an overview of oft-cited names attributed with this title.
At least three, Thomas Young, Joseph Leidy, and Athanasius Kircher, shown adjacent, have had books written about them, with the epitaph "last man to know everything" attributed or affixed to their name. 
Intellectual breaching point...MORE (15 additional contenders)
Sometime between 1700 to 1900, predominately, people began to profess the view that the body of "known knowledge" had become so large that it was no longer possible for one person to know everything. To situate this postulate in the context of a date, French philosopher Pierre Levy argues, in his 1994 Collective Intelligence, that the publication of Frenchman Denis Diderdot and Jean d’Almbert’s Encyclopedie (1751-1772) marks “the end of an area in which a single human being was able to comprehend the totality of knowledge.”
An intellectual roundtable: Friedrich Schiller (IQ=175), Wilhelm Humboldt, (IQ=175), Alexander Humboldt (IQ=185), a cited last person to know everything, and Johann Goethe (IQ=230), another well-cited last person to know everything, Jena 1797, discussing, in Goethe's own words, “all of nature from the perspectives of philosophy and science”. 
English mathematician-physicist Karl Pearson, in his science overhauling 1892 book Grammar of Science (the first book on Albert Einstein's "Olympia Academy" study group reading list) stated his view that naturalist Alexander Humboldt, pictured adjacent, was someone at the cusp of total knowledge possession (as was his associate Goethe, also pictured): 
“At the beginning of this century it was possible for an Alexander von Humboldt (1769-1859) (IQ=185) to take a survey of the entire domain of the extant science. Such a survey would be impossible for any scientist now, even if gifted with more than Humboldt’s powers. Scarcely any specialist of today is really master of all the work which has been done in his own comparatively small field. Facts and their classification have been accumulating at such a rate, that nobody seems to have leisure to recognize the relations of subgroups to the whole. It is as if individual workers in both Europe and America were bringing their stones to one great building and piling them on cementing them together without regard to any general plan or to their individual neighbor’s work.”Humboldt is one of the cited "last persons to know everything" (below); a Cattell 1000 (top 100); was one of the first to propose that South America and Africa were both joined; in 1797, in Jena, with his brother Wilhelm (IQ=175), Friedrich Schiller (IQ=175), and Johann Goethe (IQ=230), the four discussed, in Goethe's own words, “all of nature from the perspectives of philosophy and science”.
Multiple cited all-knowers | Chronological
The following group of individuals, listed in chronological order by reaction end (death), gives a listing of the known referenced opinions on the matter of who considers who to be the last person to know everything, ranked by:
(a) prevalence of citations claiming that person was the last to know everything;
(b) age of the citation, e.g. Leibniz (1914) and Young (1921);
(c) a weighting factor addition for known established IQs,
“Aristotle, described by some as the last man to know everything there was to know, wrote his classic books on rhetoric some 2300 years ago.” (1986) 
● Aristotle (384-322BC) =180
“His combined works constitute a virtual encyclopedia of Greek knowledge. It has been said that Aristotle was probably the last person to know everything there was to be known in his own time.” (2009) 
“Aristotle may have been the last person to know everything there was to be known in his own time.” (2009) 
“Roger Bacon—the founder of English philosophy whose knowledge of chemistry and mathematics led him to recognize the value of deductive reasoning, establish a scientific method, and invent spectacles—who has been called the last man to know everything, the last man to bridge the two cultures.” (2003) 
● Roger Bacon (1214-1294) IQ:175|#188
“The last person to know everything was Leonardo da Vinci.” (1985) 
● Leonardo da Vinci (1452-1519) =180
“Da Vinci, the last man to know everything, was overwhelmed by waves of depression, which left him shy and insecure.” (2004) 
Here's the EOHT homepage.
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