Ernst Heinrich Philipp August Haeckel (1834–1919) was a renowned German biologist, naturalist, philosopher, physician, professor, and artist who made substantial contributions to the field of evolutionary biology. He was born in Potsdam and later studied under Carl Gegenbaur at the University of Jena, where he eventually became a professor. Haeckel was a proponent of Charles Darwin's work and made it his mission to spread the theories of evolution and natural selection. He is often remembered for his phrase 'ontogeny recapitulates phylogeny,' encapsulating his now-outdated hypothesis that an organism's developmental process replays its species' evolutionary history. Alongside his scientific endeavors, Haeckel was a passionate artist, with his detailed drawings of flora and fauna demonstrating both his keen observational skills and his aesthetic appreciation of nature. His most notable literary work is 'The Riddle of the Universe at the close of the nineteenth century' ('Die Welträthsel', 1899), which reflects not just the knowledge of his time but also his personal philosophical worldview, influenced by monism. His style in this book, as in his other works, is marked by its combination of rigorous scientific inquiry with a vivid literary narrative, aimed at engaging a broad readership in the scientific discourse of the era. Haeckel's contributions remain pivotal in the broader cultural and scientific understanding of his time, inspiring both scientific and general audiences within the sphere of biological thought.