El único y su propiedad
The book is often considered a classic of humanism and the author's "magnum opus". Karl Marx and Friedrich Engels were strongly influenced by the book, although they criticised Feuerbach for his inconsistent espousal of materialism. Feuerbach's theory of alienation would later be used by Marx in his theory of alienation. Max Stirner directed his "The Ego and Its Own" against it. Rather than simply a polemic, Stirner's work uses Feuerbach's idea of God as a human abstraction as the basis of his critique of Feuerbach.