Roger David Casement (Irish: Ruairí Dáithí Mac Easmainn; 1 September 1864 – 3 August 1916) — known as Sir Roger Casement Kt. CMG between 1911 and shortly before his execution for treason, when he was stripped of his knighthood — was an Irish nationalist, activist, patriot and poet.
A British consul by profession, famous for his reports and activities against human rights abuses in the Congo and Peru, and also for his dealings with Germany before Ireland's Easter Rising in 1916. An Irish nationalist and Parnellite supporter in his youth, he worked in Africa for commercial interests and latterly in the service of the UK.
However, the Boer War and his consular investigation into atrocities in the Congo led Casement to anti-Imperialist and ultimately to Irish Republican and separatist political opinions. He sought to obtain German support for a rebellion in Ireland against British rule. Shortly before the Easter Rising, he landed in Ireland and was arrested. He was subsequently convicted and executed for treason. There has been controversy over a set of Black Diaries, copies of which were circulated selectively by the British authorities following Casement's conviction, which, if accepted as genuine, would portray Casement as a promiscuous homosexual with a fondness for young men. Given prevailing views on homosexuality at the time, circulation of the diaries helped undermine support for clemency for Casement.