Oskar Heinroth (1 March 1871 – 31 May 1945) was a German biologist who was one of the first to apply the methods of comparative morphology to animal behavior, and was thus one of the founders of ethology.

He worked, largely isolated from most other scientists of the period, at the Berlin Aquarium where he took care of fishes, reptiles and birds, especially waterfowl before he was murdered by Soviet occupying police agents shortly after WW2.

Heinroth was largely self taught and was not affiliated to any academic institution but his second wife Katharina had received a doctorate in 1925 under Otto Koehler (1889–1974) and together they published numerous pioneering works on animal behaviour.

[2] Lorenz regarded Heinroth as the true founder of the study of animal behavior seen as a branch of zoology.

[3][4][5] Heinroth features in the book "The Case of the 'Hail Mary' Celeste"[6] by Malcolm Pryce, particularly with reference to his work on imprinting.