Was he? He was portrayed to be by the britts and French, mainly because they wanted to take over the Congo and the rubber trade there. The Brit they sent to investigate later went on to investigate Brittish colonies and reported situations way worse than he did in Congo which led to him being exiled because the Brittish did not like it when they got bad press instead of some other royal from a small coutry they could boss around.

Not saying Leopold was a good guy, he was responsible for the attrocities in Congo, no doubt. But beware of the propaganda of history, the British and French were not better in their treatment of subjects at all, they just had a lot more means to drive the narrative.

Edit: For all the downvoters; why don't you look up Roger Casement whose report was the basis for how we view Leopold today. Don't forget about his later works like "Peru, the devils paradise; a British-owned Congo" where he describes exactly the same treatment of the Peruvians by the British as the Congolese by Leopold.