Edmund Crouchback (16 January 1245 – 5 June 1296) was a member of the royal Plantagenet Dynasty and the founder of the House of Lancaster. He was Earl of Leicester (1265–1296), Lancaster (1267–1296) and Derby (1269–1296) in England and Count Palatine of Champagne (1276–1284) in France.
Named after the 9th-century saint, Edmund was the second surviving son of King Henry III of England and Eleanor of Provence and the younger brother of King Edward I of England, to whom he was loyal as a diplomat and warrior. In 1254, the 9-year-old Edmund became involved in the "Sicilian business", in which his father accepted a papal offer granting the Kingdom of Sicily to Edmund, who made preparations to become king. However, Henry III could not provide funds for the operation, prompting the Papacy to withdraw the grant and give it to Edmund's uncle, Charles I of Anjou. The "Sicilian business" outraged the barons led by the Earl of Leicester and Edmund's uncle, Simon de Montfort, 6th Earl of Leicester, and was cited as one of the reasons for limiting Henry's power. Deterioration of relations between the barons and the king resulted in the Second Barons' War, in which the royal government, supported by Edmund, triumphed over the baronage following the death of Montfort in the Battle of Evesham in 1265.