Who is Roger David Casement from King Leopold's Ghost and what is their importance?

Roger David Casement (1864 - 1916) was a British consul, an Irish patriot, and a revolutionary. In his youth Casement was an Irish nationalist, though he worked in Africa for commercial concerns and, later, in the British consular services. He had spent some time in the Congo without making much comment on various atrocities before being commissioned, in 1903, to conduct an investigation throughout the Congo of alleged widespread atrocities and human rights abuses.