Heinrich Ernst Karl Jordan (7 December 1861 – 12 January 1959) was a German-British entomologist.
Jordan was born in Hanover and educated at Göttingen University. In 1893 he began work at Walter Rothschild's Natural History Museum at Tring, specialising in Coleoptera, Lepidoptera and Siphonaptera. Jordan published over 400 papers, many jointly with Charles and Walter Rothschild. He described 2,575 new species himself, with an additional 851 in collaboration with the Rothschilds.
Jordan initiated and founded the first International Entomological Congress, held in 1910. He became a naturalized British citizen in 1911. Jordan was a fellow of the Royal Society, and president of the Entomological Society of London from 1929 to 1930.
Jordan is commemorated in the scientific name of a species of African lizard, Karusasaurus jordani.
In 1972, the Lepidopterists' Society began to award the Karl Jordan Medal in his honour.
- Rothschild, Miriam (1983). Dear Lord Rothschild: Birds, Butterflies and History. London: Hutchinson. 398 pp. ISBN 0-09-153740-1.
- Johnson, Kristin (2012). Ordering Life: Karl Jordan and the Naturalist Tradition Baltimore: Johns Hopkins University Press. viii + 376 pp. ISBN 978-1-4214-0600-8 (hardcover), ISBN 978-1-4214-0650-3 (electronic). ISBN 1-4214-0600-4 (hardcover), ISBN 1-4214-0650-0 (electronic).