Julius Friedrich Leopold Rupp (13 August 1809 – 11 July 1884) was a Prussian Protestant theologian.

He founded the first Free Protestant Congregation in Königsberg, which rejected all state or church control and believed in absolute freedom of conscience for its members.

Julius Rupp studied theology and philosophy at the University of Königsberg 1827–30, and was a student of Johann Friedrich Herbart.

[2] In 1837 he published a summary of universal history for the higher classes at the gymnasium, including genealogical tables and maps.

[11] In late 1845 Rupp delivered a sermon to several hundred people in which he challenged the right of the government to enforce the official creed.

[2] After violent conflict with the ecclesiastical and civil authorities Rupp finally resigned in January 1846 as preacher.

[3] Despite his dismissal, Rupp said he still considered himself a Protestant minister, since the church was a Christian community and not a state institution.

Some of his liberal supporters organized a Free Congregation (freie Gemeinde) and elected Rupp as chief preacher.

Gustav Adolf Wislicenus gave the view of the radicals in an open letter in which he stated that the free congregations represented a complete break with the past.

[11] The congregation was organized by evangelical principles and wanted to be free of all government coercion and all supervision by church authority.

At this time Rupp wrote a circular letter to the Evangelican Church in Germany on the question, Creeds, or God's Word?.

He and other liberals also published a periodical named Free Evangelical Church (Die Freie Evangelische Kirche).

[2] Despite many obstacles other congregations were formed in Memel, Domnau, Kreuzburg, Preußisch Eylau, and later in Schneidemühl, Elbing, Danzig and Tilsit.

The will of the transcendent God was primarily defined in terms of ethics, and had been communicated in the teachings of Christ as recorded in the Gospel of Matthew.

A Christian should be committed to embodying these ethical values, which included freedom, justice, equality and love.

"[20] Rupp's son-in-law Carl Schmidt took over the position of pastor of the Free Protestant Congregation in Königsberg.

[19] Emma Ihrer was active in the Free Religious Congregation in the 1870s and 1880s, as were other founders of early socialist women's organization in Berlin such as Ottilie Baader and Agnes Wabnitz.

[15] In 1909 the Freie evangelische Gemeinde installed a memorial stone with a bronze portrait of Rupp by Käthe Kollwitz in front of his house at Pauperhausplatz 5 in Königsberg.