Bruno Bauer (/ˈbaʊər/; German: [baʊɐ]; 6 September 1809 – 13 April 1882) was a German philosopher, theologian, historian, and biblical critic. A prominent member of the Young Hegelians, he was a radical rationalist critic of the Bible and Christianity. Initially a student of Georg Wilhelm Friedrich Hegel, Bauer became a central figure in the intellectual circles of the Vormärz, the period preceding the Revolutions of 1848. His philosophical work was a major influence on, and target of critique for, Karl Marx and Friedrich Engels, with whom he had a close but tumultuous relationship.

Starting as a right-wing Hegelian, Bauer shifted to the left in 1839, developing a radical critique of religion and the state. He argued that the Christian gospels were not historical records but literary works of the human self-consciousness. His most significant work of this period, The Trumpet of the Last Judgement over Hegel the Atheist and Antichrist (1841), presented Hegel's philosophy as a revolutionary atheism that called for the overthrow of all existing religious and political institutions. Bauer's political thought was a form of republicanism based on the concept of "infinite self-consciousness," an ethical idealism that advocated for the constant transformation of society in pursuit of rational freedom.

During the 1840s, Bauer engaged with the emerging social question, developing a critique of both liberalism, for its basis in private interest, and the nascent socialist movements. His controversial writings on Jewish emancipation, in which he argued that both Jews and Christians must renounce their particular religious identities to achieve universal freedom, led to his isolation from many of his former allies. Though he participated in the 1848 Revolutions, their failure led him to abandon his revolutionary republicanism and turn to conservative causes.

In his later life, Bauer developed a virulent anti-Semitism. His post-1848 work focused on historical studies, particularly the origins of Christianity, and on the political development of Russia and the rise of global imperialism. Despite the profound change in his political orientation, his work continued to influence thinkers on both the left and the right, including Karl Kautsky and Friedrich Nietzsche.

Bruno Bauer was born on 6 September 1809 in Eisenberg, Thuringia. His father was a porcelain painter, and the family moved to Berlin in 1815. In 1828, Bauer enrolled as a theology student at the University of Berlin, where he studied under Georg Wilhelm Friedrich Hegel himself for three years, as well as Hegel's associates Philipp Marheineke and Henrik Steffens. Bauer was particularly disappointed with the teachings of Friedrich Schleiermacher, whose attempts to find a compromise between various conflicting schools of thought seemed to Bauer to engender only ambiguity and uncertainty.

In 1829, while still a student, Bauer won the annual Royal Prize in Philosophy on Hegel's recommendation for an essay on Immanuel Kant's aesthetics. Hegel lavished praise on the work, stating: "The lecture [...] develops most convincingly [...] there is consistent development of the thought and the author has also succeeded in exploiting the contradictions of the Kantian principles, which are incompatible." After graduating in 1832, Bauer began an academic career in theology. He became a close associate of the Hegelian school, and was entrusted with editing the second edition of Hegel's Lectures on the Philosophy of Religion (1840). He taught at Berlin from 1834 to 1839, delivering lectures on theology, the Bible, and church history, and serving as the main editor for the Zeitschrift für spekulative Theologie (Journal for Speculative Theology). During this period, his work was imbued with a spirit of conservative orthodoxy. This led him to be chosen to write the official critique of David Strauss's sensational 1835 book The Life of Jesus, in which he initially defended the historicity of the Gospels.

By 1839, Bauer had made a decisive shift to a Left Hegelian position, marked by a public break with conservative orthodoxy in his polemical work Herr Dr. Hengstenberg. In this work and others, he defended the progressive character of Hegel's system and separated the "spirit of Christianity" from its dogmatic form, undermining the religious ideology of the Prussian Restoration. This turn was influenced by his involvement with the Berlin Doktorklub (Doctors' Club), an intellectual circle of Young Hegelians that included Karl Marx, Friedrich Köppen, and others. Bauer was considered the moving spirit of this group. His increasingly radical views led the Prussian Minister of Culture, Karl vom Stein zum Altenstein, to move him to the University of Bonn in an effort to shield him from attacks in Berlin.

Bauer's radicalization intensified with his critiques of the Gospels, which he developed over a series of works from 1840 to 1842. The project began with his Critique of the Gospel of John (1840), followed by the three-volume Critique of the Synoptic Gospels (1841–42). In these works, Bauer argued that the Gospel narratives were not historical reports of the life of Jesus, but literary products of the religious consciousness of the early Christian community. He saw the evangelists not as historians but as artists who had transformed earlier religious traditions into a new, dogmatic form. He concluded that the figure of Jesus was a literary invention, a transplantation of the community's own struggles and experiences onto a single representative figure. This critique was aimed directly at the ideological foundations of the Prussian state, which used dogmatic Christianity for its legitimation.