Ferdinand I, 1345–83, king of Portugal (1367–83), son and successor of Peter I. His ambitions and his private life plunged the realm into disaster, although during his reign agricultural reform was achieved and Portuguese commercial power grew. Ferdinand's desire for the throne of Castile involved him in three wars with Castile. The first (1369–71) ended with Ferdinand's promise to marry Leonor, daughter of Henry II of Castile. Instead he fell in love with a Portuguese noblewoman, Leonor Teles, and after securing a dubious annulment of her earlier marriage, made her his queen. Ferdinand then allied (1372) himself with John of Gaunt and waged new war against Henry II, which led to a Castilian siege of Lisbon (1373) and a humiliating peace. After John I succeeded to the throne of Castile, Ferdinand, under the influence of his wife and her lover (the conde de Ourém), resumed the English alliance and engaged (1381–82) in a third humiliating war with Castile. It was concluded by the marriage of John with Ferdinand's daughter and heiress, Beatrice. Portugal would thus have gone to Castile on Ferdinand's death, but a national revolution gave the throne to Ferdinand's half-brother, John I.
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