Paul-Henri Thiry, Baron d'Holbach, known as d'Holbach, was a Franco-German philosopher, encyclopedist and writer, who was a prominent figure in the French Enlightenment. He was born Paul Heinrich Dietrich in Edesheim, near Landau in the Rhenish Palatinate, but lived and worked mainly in Paris, where he kept a salon. He helped in the dissemination of "Protestant and especially German thought", particularly in the field of the sciences, but was best known for his atheism and for his voluminous writings against religion, the most famous of them being The System of Nature (1770) and The Universal Morality (1776).

Atheism, in the broadest sense, is an absence of belief in the existence of deities. Less broadly, atheism is a rejection of the belief that any deities exist. In an even narrower sense, atheism is specifically the position that there are no deities. Atheism is contrasted with theism, which in its most general form is the belief that at least one deity exists.