If you're not a libertarian (and maybe even if you are), Anthony de Jasay is possibly the greatest thinker you have never heard of.
A reason for that might be that de Jasay (who just turned 90 on October 15) was an academic outsider. Though in his youth he was a research fellow at Nuffield College, Oxford, later on his career was spent in banking and finance. He started writing on political philosophy after retiring. He is thus a most rare animal, in the contemporary world: a gentleman scholar.
Another reason for the relative neglect of de Jasay among contemporary political philosophers could be the fact that he never fully subscribed to any particular "school" of thought. A cold-blooded, realistic thinker, de Jasay was never terribly interested in building a following. There is no consensus on how he's best described. A Humean libertarian? A reluctant anarchist? A conservative anarchist?
Karl-Peter Schwarz celebrated de Jasay's birthday in the Frankfurter Allgemeine Sonntagszeitung. The Independent Review, in its Summer issue, provides us with a symposium in de Jasay, edited by G. Patrick Lynch (who also points out that de Jasay is "difficult to categorize"). The symposium includes, after an introduction by Pat Lynch, contributions by Hartmut Kliemt, Pierre Lemieux, Andre' Acevedo Alves, Carlo Ludovico Cordasco and Sebastiano Bavetta, and David H. Hart. The symposium is sort of completed by a fine review of de Jasay's last collection of essays, Social Justice and the Indian Rope Trick, written by Michael Munger and included in the review section.
I found Pierre Lemieux's and David Hart's essays particularly noteworthy. When de Jasay published The State, in 1985, the book was praised by James Buchanan (see here the Buchanan's review). Lemieux compares De Jasay's work with the tenets of public choice theory. There are similarities "including a common individualist methodology, the same normative individualist presumption, the nonromantic analysis of government, and the rejection of any 'social welfare function' and cost-benefit analysis". But "the state can be conceived as a servant or as a dominator. Public-choice theory adopts the first conception (...) The State defends the second conception".
David Hart quotes Molinari's despair: that great French economist was depressed because "hardly anyone listens to economists". Therefore thinkers like Molinari got into popular writings because people tend to miss several, economic counter-intuitive truths: Adam Smith debunked the mercantilist fallacy, Bastiat "guillotined the idea that natural disasters (...) can have a 'silver lining' in the rebuilding of a destroyed city." And yet these ideas endure in the popular discussion.
Hart's thoughtful essay is part of a longer research project on the popularisation of classical liberal ideas. He carefully considers de Jasay's popular works, many of which are published on this same website. Hart draws an explicit comparison between de Jasay and Bastiat, who also authored an essay on The State.
Of de Jasay's popular writings, published by EconLib, some, as Hart underlines, are truly micro-classic. If you didn't yet, read "Your Dog Owns Your House" ( a little classic), the series on "Finance in Parrot Talk" and "Is Society a Great Credit Card?". The latter, I think, it is a particularly noteworthy one. De Jasay is a very precise writer. But he is also a champion of effective, pictorial prose. Famously, in The State he explained that classical liberal constitutionalism failed in limiting government by saying that Constitutions are like chastity belts whose key is always within reach. On Econlib, he points out that public finance is different in democracies than it used to be: typically, kings got indebted in wars but also balanced the budget every ten years or so, now "big budget deficits in rough times alternate with smaller ones in better days". We got used to consider the state as a "great credit card" indeed.