Eccentric geniuses in literature - why so few?

Wracking my brain, trying to think of truly genius and eccentric characters in fiction - narrators don't count - as it's (relatively) easy to have a genius narrator, in that the n's observations, quips, queries are actually the writer's and they can take place in abstract time - in other words, the narrator's observations can be far removed from the events of the plot - whereas a character has to live within the timeframe of the plot. To create an eccentric-genius character, the writer has to "equip" the character with brilliant observations and strange behavior that feels, within the borders of the story, natural and credible. Some of the v. few examples that come to mind could be: Mann's Setembrini, Joyce's Dedalus, Roth's Zuckerman maybe?, McPhee's dominant father in Beautiful Lies maybe?, the lead character in Confederacy of Dunces maybe? These, however, either push the needle too far toward eccentric and away from genius - or else are clearly authorial standins (Setembrini being the exception). In other words - to create a genius character the author must be a genius as well, or at least must have observed a lot of geniuses. This issue comes up now as I've started Andre Aciman's novel Harvard Square - which begins with a dad taking son on college tour of Harvard, son, feeling pressured by alum Dad besotted with his own memories of the place, wants to leave - and then Dad/narrator/Aciman? (narrator is unnamed) reflects back on his grad-school days at Harvard, during which he felt lonely and somewhat like an outsider, as a foreign student from Alexandria (Egypt), Jewish of French parentage, thus twice removed from his native language and culture. He recalls studying for his qualifying exams, spending many hours and as little $ as possible in coffee shops, at one of which (Cafe Algiers - Aciman is very true to the place names and so forth of Cambridge - though he seems to have invented names of Harvard faculty members) he meets a fellow North African/French refugee, Kalaj (pronounced College?) - in the midst of a bitter intellectual debate about the plasticity of American culture, to which K. attaches his favorite descriptor, "ersatz." Aciman's success, if the relation between K. and narrator will remain central, will depend upon how credible he can make K. - he's memorable in the first scene, the coffee shop encounter, but not nearly so brilliant as he thinks himself to be - nor as the narrator, at least at this point, thinks - his rant really a pastiche of undergraduate cynicism, but maybe he will evolve as A. reveals - or learns - more about him and his background. He's eccentric for sure - but not, based on what A. has him saying in the coffee shop, a genius exactly - not even an original thinker.