John I (August 24 1358 – October 9, 1390) (in Spanish: Juan I) was the 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.

His first marriage, with Eleanor of Aragon, produced most of his issue, including sons Enrique (Henry) and Fernando de Antequera (Ferdinand).

He had engaged in hostilities with Portugal. His first quarrel with Portugal was settled by his marriage, in 1382, with Beatrice of Portugal, daughter of King Ferdinand I of Portugal. 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. The 1383-1385 Crisis, a period of civil unrest and anarchy in Portugal, followed. He was resisted by the national sentiment of the Portuguese people, and was utterly defeated at the battle of Aljubarrota, on August 14, 1385.

He also had to contend with the hostility of John of Gaunt, who claimed the crown by right of his wife Constance, the eldest 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 Constance and John of Gaunt in 1387.

King John was killed at Alcalá on October 9, 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.

References

Castilian monarchs | 1358 births | 1390 deaths

Joan I de Castella | Johann I. (Kastilien) | Juan I de Castilla | Jean Ier de Castille | Giovanni I di Castiglia | Johan I van Kastilië | フアン1世 (カスティーリャ王) | Jan I (król Kastylii i Leónu) | João I de Castela | Хуан I Кастильский | Juhana I (Kastilia)