George Washington Williams was one of the first people to publicly describe the atrocities being carried out in the Congo Free State under King Leopold II of Belgium. But so much happened in his life before that.
Research:

Robert Moses and the Shaping of New York, Part 1
41:59

SYMHC Classics: Eradication of Smallpox
43:25

Behind the Scenes Minis: Progressive Medicine
22:11