Holbach, Paul Henri Thiry, baron d', Ger. Paul Heinrich Dietrich, Baron von Holbach, 1723-89, French philosopher, one of the Encyclopedists. Although a native of the Palatinate, he lived in Paris from childhood. He became a member of a group of notable thinkers and literary men including Diderot, Helvétius, Condorcet, and Rousseau. A supporter of naturalistic and materialistic views, he was a vigorous opponent of Christianity and all positive forms of religion. His best-known work is Système de la nature (1770), first published under the name of Mirabaud.