Short answers, pulled from the story.
The Congo Free State was a large state and absolute monarchy in Central Africa that existed from 1885 to 1908. It was privately owned by King Leopold II of Belgium, who controlled it from Brussels and never visited it. It was not part of Belgium; the two were joined only in a personal union.
Leopold II convinced European powers at the Berlin Conference that his work was humanitarian and that he would not tax trade. Through the International Association of the Congo he claimed most of the Congo Basin. On the 29th of May 1885 he announced the name Congo Free State, which officially replaced the International Association of the Congo on the 1st of August 1885.
Leopold's administration used forced labour, torture, and murder to extract ivory, rubber, and minerals. The Force Publique enforced rubber quotas with the chicotte whip, took hostages, burned villages, and cut off the hands of Congolese people, including children, as proof that bullets had not been wasted. These atrocities made it one of the greatest international scandals of the early 20th century.
British Consul Roger Casement investigated and produced the Casement Report in 1904, and journalist E. D. Morel campaigned against the regime and co-founded the Congo Reform Association with him. Members included Sir Arthur Conan Doyle, Mark Twain, Joseph Conrad, Booker T. Washington, and Bertrand Russell, and Conrad's novel Heart of Darkness drew international attention.
Estimates vary widely and no reliable census exists from the period's start, since the first was taken in 1924. A 1919 Belgian commission and studies cited by Adam Hochschild concluded roughly half the population died, with figures such as 10 million cited. Recent demographic research estimates the 1885 population at most likely 11.5 million and a decline of around 1.2 to 1.5 million.
The Belgian Parliament annexed the Congo Free State on the 15th of November 1908, governing it thereafter as the Belgian Congo under the 1908 Colonial Charter. The annexation followed public pressure and international scrutiny. Leopold II died in Brussels on the 17th of December 1909.