This biographical monograph explores the scientific life and contributions of Reinhard Dohrn (1880–1962), a key figure in early 20th-century German zoology and marine biology. The volume traces his role in managing the Stazione Zoologica in Naples, emphasizing his work in systematics, embryology, and comparative anatomy. It situates Dohrn within the broader context of European scientific institutions and addresses the impact of political changes on academic research. The book is structured as both a personal and professional account, with archival materials and correspondences enriching its historical-scientific perspective.