[W]hen mystery writers have looked for a real historical figure to add gravitas to their novels, they've usually gone for the very mighty, from Julius Caesar in Steven Saylor's Rubicon to John F Kennedy in James Ellroy's American Tabloid. This makes sense - a lot of murders are about power - but what's much more interesting is the clash between the brutal, messy world and someone who lives mostly in their own gentle, ordered mind, like a philosopher or a novelist.Beauman mentions other writers and philosophers who appear in fictional roles--including Kant, Chaucer, Shakespeare, Defoe, Dickens, Wilkie Collins, Mark Twain, Poe, Jane Austen and Beatrix Potter--before naming the philosopher he'd like to see as a mystery-solver.
The supreme example of this is probably an out-of-print, 1978 novel called The Case of the Philosopher's Ring by Randall Collins, in which Bertrand Russell despatches Sherlock Holmes to find out who has stolen Wittgenstein's mind.
--Marshal Zeringue