Dr Alwin Karl Haagner (1880-1962) was a South African ornithologist.
Haagner worked in the Transvaal Museum from 1906, where he started the museum's great ornithological collection. Haagner left the museum in 1911, was succeeded by Austin Roberts, and became director of the Pretoria Zoological Gardens.
He took an interest in the Kruger National Park and played an important role in drafting the National Parks Acts of 1926. He was the author of Sketches of South African Bird-Life.
Haagner compiled A Checklist of the Birds of South Africa with J. W. B. Gunning, first director of the Transvaal Museum in 1910.