The person responsible for the assassination of the Archduke Franz Ferdinand that sparked World War I was Gavrilo Princip, a Bosnian Serb nationalist. His actions on June 28, 1914, in Sarajevo set off a chain of events leading to the outbreak of the war. His assassination was politically motivated, aiming to challenge Austro-Hungarian rule over Bosnia. This act of violence highlighted the escalating tensions between nationalist movements and imperial powers, which ultimately contributed to the extensive network of alliances that led to global conflict.