German zoologist and teacher who initiated the modern science of parasitology. He described the complicated life histories of various parasites, including tapeworms and the liver fluke, and demonstrated that some human diseases, such as trichinosis, are caused by multicellular animals of the various wormlike phyla. His textbook, Die menschlichen Parasiten (1863–76; Eng. trans., The Parasites of Man, 1886), was of fundamental importance; he also wrote many scientific papers.

Though remembered primarily for his work in parasitology, Leuckart did other innovative work in zoology; for example, in systematics he showed that the radial symmetry of the coelenterates (such as jellyfish) and echinoderms (starfish) did not indicate a close relationship between the two groups.

He taught successively at the universities of Göttingen (where he was educated), Giessen, and Leipzig.