Fernando I of Portugal

Ferdinand I
Miniature of Ferdinand I during the Fernandine Wars, in Jean de Wavrin's Chronique d'Angleterre
King of Portugal and the Algarve
Reign	18 January 1367 – 22 October 1383
Predecessor	Peter I
Successor	John I
King of Castile (in Galicia) in opposition to Henry II
Reign	23 March 1369 – 31 March 1371
Predecessor	Peter I
Successor	Henry II
Born	31 October 1345 (1345-10-31) Coimbra, Portugal
Died	22 October 1383 (1383-10-23) (aged 37) Lisbon, Portugal
Burial	Carmo Convent, Lisbon
Spouse	Leonor Teles
Issue among others...	Beatrice of Portugal
House	Burgundy
Father	Peter I
Mother	Constanza Manuel
Religion	Roman Catholicism

Dom Ferdinand I (Portuguese: Fernando; 31 October 1345 – 22 October 1383), sometimes called the Handsome (o Formoso or o Belo ) or occasionally the Inconstant (o Inconstante), was the King of Portugal and the Algarve from 1367 until his death in 1383. His death led to the 1383–85 crisis, also known as the Portuguese interregnum.

Ferdinand was born in Coimbra, the second but eldest surviving son of Peter I and his wife, Constanza Manuel. On the death of Peter of Castile in 1369, Ferdinand, as great-grandson of Sancho IV by the female line, laid claim to the vacant Castilian throne. The kings of Aragon and Navarre, and later John of Gaunt, Duke of Lancaster, who had married Peter of Castile's eldest daughter, Constance, also claimed the throne.

The throne was held by Henry of Trastámara (Henry II of Castile), Peter of Castile's illegitimate brother, who had defeated him in the Castilian Civil War in 1366 and assumed the crown. After one or two indecisive campaigns, all parties were ready to accept the mediation of Pope Gregory XI. The conditions of the treaty, ratified in 1371, included a marriage between Ferdinand and Leonora of Castile. But before the union could take place Ferdinand had become passionately attached to Leonor Telles de Meneses, the wife of one of his own courtiers. Having procured a dissolution of her previous marriage, he lost no time in making Leonor his queen.

This conduct, although it raised a serious insurrection in Portugal, did not at once result in a war with Henry. However, the outward concord was soon disturbed by intrigues with the Duke of Lancaster, who entered into a secret treaty with Ferdinand for the expulsion of Henry from his throne. The war which followed was unsuccessful; and peace was again made in 1373.