Hermann Fol was a very accomplished Swiss naturalist of the late 19th century, but today is largely forgotten. He was a student of the notable biologists Edouard Claparéde and Ernst Haeckel, and like them, specialized in the study of marine organisms. Fol is known only among embryologists for his description of fertilization in echinoderms. In reality, his work ranged well beyond such studies to encompass diverse taxa of the marine plankton, illustrated with remarkable scientific artwork, and included designing various scientific devices. Fol worked on human embryology, light penetration in seawater, methods of reducing microbial contamination of drinking water, and development of a rabies vaccine. His career was marked by a long series of disputes with contemporary naturalists (including Alfred Giard) and was relatively short, ending at age 47 with a mysterious disappearance. I provide a review of his contentious life, his scientific work, his scientific art, his scientific inventions, and his role in establishing Villefranche-sur-Mer as a center of marine science.The life and work of Hermann Fol is shown to be an example of the very wide ranging activities of 19th century naturalists, and the apparent dangers of an over-sized ego.