The Congo was a personal possession of the King of Belgium, who styled himself Emperor. Under his direct rule the Congolese suffered as complete slaves until the colony was brought under the rule of the Belgian government.
The Belgian Congo was what the Congo was called before they gained independence. Basically, King Leopold from Belgium declared the Congo his own property (not Belgium's) and many from his kingdom...
In the colonial age, every western country had to have a colony to be "in". Belgium became a part of King Leopold II PERSONAL treasure, it was called belgian Congo, but actually it was his personal...
In 1960 Belgium granted Congo independence after it held a conference in Brussels. They tried to negotiate terms but the Congolese wanted independence quickly.