Johannes Fastenrath was born on 3 May 1839 as the only son of a wealthy merchant family in Remscheid. In 1847 he moved to Cologne. Fastenrath attended the Friedrich-Wilhelm-Gymnasium in Cologne and studied law at the Universities of Bonn, Heidelberg, Munich, Paris and Berlin. After completing his doctorate at the University of Berlin, Fastenrath began his legal clerkship at Cologne Regional Court. As a wealthy man by birth, Fastenrath soon withdrew from the legal profession and travelled extensively. He devoted himself to his life's work, mediating between the German and Spanish cultural nations. In Cologne, Fastenrath was actively involved in the founding of the Literary Society in 1893. He was elected First Chairman and held this position until 1908. In addition to poetry readings and lecture evenings, the "Kölner Blumenspiele ", a sort of annual romantic poetry competition, should be mentioned above all. The Fastenraths also supported the Cologne Carnival. On 16 March 1908 Johannes Fastenrath died of pneumonia in Cologne.

Fastenrath had already taken history and linguistics as minor subjects during his studies. In Bonn he attended the lectures of the Romanist Friedrich Diez (1794-1876). With his later congenial wife, the writer Luise Goldmann, Johannes Fastenrath translated, edited and wrote Spanish works and promoted Spanish literature in many ways. The Fastenraths, however, did not only support the artists, they also provided generous help for the victims of the devastating natural disasters (floods, earthquakes) and the plague epidemic that struck Spain in the second half of the 19th century. Fastenrath received special respect for his commitment. On the occasion of his death, several Spanish journals wrote obituaries. The Spanish king Alfonso XIII condoled the widow and thanked her for the legacies of German and Spanish writers. From 1909 the "Fastenrath Prize" was awarded at the "Jocs Florals" in Barcelona. Johannes Fastenrath's main work "La Walhalla y las glorias de Alemania" (1872, 1910) was intended to promote the achievements of German culture in Spain.


 "Die Bibliothek sei der Stadt Köln als Andenken an mich" zu übergeben (The library is to be handed over to the City of Cologne as a memento of myself). This was the will of Johannes Fastenrath. The donation to the City Library comprised around 10.000 volumes of literature from Romanesque countries, including a considerable number of books on Spanish literature, history and regional studies. After the duplicates had been sorted out, the books were transferred to the classification system, which was structured according to subjects. With the municipal library, the volumes were transferred to the UCL, which was newly created in 1920. Fastenrath's books have a particularly magnificent ex-libris. It shows two female figures standing on a pedestal, representing the embodiment of Spain and Cologne. They represent the Fastenrath couple's intense friendship with Spain.