Hegel by Popper
Popper's Hegel is the most loathsome of philosophers. He was the court philosopher of Fredrick Wilhelm III of Prussia and as such, his primary impulse was to justify the monarch's absolutism in a world turning against it. Many diseases of German politics and history can be traced to him - the fascism, the racism, the bellicosity that plunged the world into two global wars and shattered the German empires.
An obscurantist and a charlatan, he poisoned generations of German philosophy. Not least of his crimes, I imagine, is his role in inspiring Marx, but I haven't gotten that far in the book yet.