Karl August Neunzig was a German illustrator and editor of the specialist magazine Gefiederte Welt from 1900 to 1938.

Karl Neunzig attended the Academy of Fine Arts in Berlin. He initially devoted himself to landscape painting and later to depicting animals, especially birds. His drawing of the Spix's macaw is famous.

Karl Ruß recruited Neunzig to illustrate the specialist journal Gefiederte Welt, which he took over as editor after Ruß's death in 1899. For decades, he published numerous articles and very good bird pictures in Gefiederte Welt, especially husbandry reports on exotic birds. He used popular ornithology to focus attention on bird and nature conservation. He also edited Karl Ruß's Handbuch für Vogelliebhaber (Handbook for Bird Lovers), which was published in two volumes: Fremdländische Stubenvögel (5th edition 1921) and Einheimische Stubenvögel (4th, 5th, 6th editions 1904, 1913, 1922). Neunzig did not live to see the fall of the Nazi empire, in which he was ostracized for not being completely loyal to the Nazi line.