Ernst Haeckel was a distinguished German biologist, naturalist, and artist who discovered, described, and named thousands of new species. He mapped a genealogical tree relating all life forms and coined many terms in biology, including ecology, phylum, and stem cell. Haeckel promoted and popularized Charles Darwin's work in Germany and developed the controversial recapitulation theory, famously summarized as 'ontogeny recapitulates phylogeny'. His artistic work, particularly the volume 'Kunstformen der Natur' (Art Forms in Nature), influenced artists and designers of the early 20th century with its detailed illustrations of biological organisms.