Wasn't limited to Leopold, though his Stalinesque reputation means his is probably one of the better known. Many of the "developed" nations of the late 1800s and early 1900s had ethic villages or exhibitions - with live exhibits. London, Paris, New York, etc. St Louis made a point of adding newly acquired native Philippinos to the native American display at the World Fair and 1904 Olympics. Developed nations carried on with those exhibitions far longer than you might expect or hope. Though they were in decline by WW2, there's been a fair selection of basically racist exhibits post war.
https://en.wikipedia.org/wiki/Human_zoo
King Leopold II was a bit special, even by the standards of the height of colonialism. His privately owned Congo Free State - it really was his, founded and owned by him personally was excessively bad at everything. It started public and government campaigns in Britain, America and I believe France and others too, ultimately culminating in multiple nations taking stand and signing treaties against Leopold's vanity project. The atrocities were far in excess of any other colonial power for the few years he owned it. Millions died, millions more, including children, had hands or feet hacked off. The state stepped in and it became the Belgian Congo after 15 or 20 years of Stalin ^W Leopold. (Edit: In that time, the 1919 Belgian Government Commission estimated half the population had died).
https://en.wikipedia.org/wiki/Congo_Free_State
Belgium has been surprisingly reluctant to even acknowledge this black spot in their history, and you will still find plenty of statues, squares and streets in his honour.
Should you want to read more, and it's not an easy read, I'd recommend King Leopold's Ghost by Adam Hochschild.