1911 Encyclopædia Britannica/John I. of Castile
JOHN I. (1358–1390), king of Castile, was the son of Henry II., and of his wife Joan, daughter of John Manuel of Villena, head of a younger branch of the royal house of Castile. In the beginning of his reign he had to contend with the hostility of John of Gaunt, who claimed the crown by right of his wife Constance, daughter of Peter the Cruel. The king of Castile finally bought off the claim of his English competitor by arranging a marriage between his son Henry and Catherine, daughter of John of Gaunt, in 1387. Before this date he had been engaged in hostilities with Portugal which was in alliance with John of Gaunt. His first quarrel with Portugal was settled by his marriage, in 1382, with Beatrix, daughter of the Portuguese king Ferdinand. On the death of his father-in-law in 1383, John endeavoured to enforce the claims of his wife, Ferdinand's only child, to the crown of Portugal. He was resisted by the national sentiment of the people, and was utterly defeated at the battle of Aljubarrota, on the 14th of August 1385. King John was killed at Alcalá on the 9th of October 1390 by the fall of his horse, while he was riding in a fantasia with some of the light horsemen known as the farfanes, who were mounted and equipped in the Arab style.