Oskar Heinroth (Mainz-Kastel, 1 March 1871 – Berlin, 31 May 1945) was a German biologist who was one of the founders of ethology. Heinroth was director of the Berlin Zoo & Aquarium for over 30 years. He married twice, both times to colleagues: He was married to Magdalena (née Wiebe, 1904-1932) and, after her death, to Katharina (née Berger, 1933-1945).