Dom Ferdinand I (Portuguese: Fernando) sometimes called the Handsome (o Formoso or o Belo ) or occasionally the Inconstant (o Inconstante), was the King of the Kingdom of Portugal from 1367 until his death in 1383. His death led to the 1383-85 crisis, also known as the Portuguese interregnum.
Ferdinand left no male heir when he died at Lisbon on 22 October 1383, and the direct Burgundian line, which had been in possession of the throne since the days of Count Henry (about 1112), became extinct. The stipulations of the treaty of Badajoz were set aside, and John, Grand Master of the order of Aviz, Ferdinand's illegitimate brother, claimed the throne. This led to a period of war and political indefinition known as the 1383-1385 Crisis. John became the first king of the House of Aviz in 1385.
Ferdinand's spectacular ornate tomb can be found on display at the Carmo Archaeological Museum in Lisbon.