What parts of Africa did King Leopold II of Belgium colonize?
The Congo River Basin area in central Africa.
The area was run as a Colonial State owned by King Leopold personally and devoted to natural resource extraction by brutally exploiting the local people. The Belgian government was leery of colonial adventures at the time (1885) and Leopold colonized it on his own.
It was financially very successful for Leopold but eventually word got out about the level brutality involved and the Belgian Government was forced to take over (1908).
The area was expanded slightly after World War 1 to include the former German controlled area of present day Rwanda and Burundi.
The area is very rich in natural resources and an area of continuing conflict today.