Ernest Belfort Bax (23 July 1854 – 26 November 1926) was a British socialist, journalist and philosopher. Born into a nonconformist religious family in Leamington, he was first introduced to Marxism while studying philosophy in Germany. He combined Karl Marx's ideas with those of Immanuel Kant, Arthur Schopenhauer and Eduard von Hartmann. Keen to explore possible metaphysical and ethical implications of socialism, he came to describe a "religion of socialism" as a means to overcome the dichotomy between the personal and the social, and also that between the cognitive and the emotional. He saw this as a replacement for organised religion, and was a fervent atheist, keen to free workers from what he saw as the moralism of the petty bourgeoisie.

Bax wrote a historical narrative about the Peasants War in Germany, the largest popular uprising in European history aside from the French Revolution). Despite its size, it has mostly been forgotten historically. Friedrich Engels wrote about it in 1850 from a Communist/Socialist perspective, and the Nazis often referenced it. Bax gives a narrative of the battles and individuals involved in the uprising. Bax wrote several books about Socialism and important historical events, including the French Revolution. In The Religion of Socialism, published in 1886, Bax discusses socialism at length in a series of related essays.