João I, tenth king of Portugal (in English, John I) (the Good or sometimes, the Great or even the One With Good Memory), was born in Lisbon in April 11 1357 and died in the same city in August 14 1433. He was the natural son of Pedro I by a noble Galician lady called Teresa Lourenço. In 1364 was created grand-master of the Order of Aviz. He became king of Portugal in 1385, after the 1383-1385 Crisis.

On the death of his lawful brother Fernando in October 1383, without a male heir, strenuous efforts were made to secure the succession for princess Beatrice, his only daughter. As heiress-apparent Beatrice had been married to king John I of Castile, but the popular voice declared against an arrangement by which Portugal would virtually have become united with Castille. The 1383-1385 Crisis followed as a period of political anarchy, when no king ruled the country.

Finally in April 6 1385, the council of the kingdom (cortes in Portuguese) summoned in Coimbra declared João, then Master of Aviz, king of Portugal. This was in effect a declaration of war against Castile and its pretensions to the Portuguese throne. Soon after, the king of Castile invaded Portugal, with the purpose of conquer Lisbon and remove João I from the throne. Juan I was accompanied by French allied cavalry as English troops and generals took the side of João (see Hundred years war). João I then named Nuno Alvares Pereira, his loyal and talented supporter, general and protector of the kingdom. The invasion was repelled during the Summer after the battle of Atoleiros, but especially after the decisive battle of Aljubarrota (August 14, 1385), where the Castilian army was virtually annihilated. Juan I of Castile then retreated and the stability of João I's throne was permanently secured.

In 1387, João I married Philippa of Lancaster, daughter of John of Gaunt who had proved to be a worthy ally, consolidating with this union the English-Portuguese alliance that endures to present day.

After the death of Juan of Castile died, without leaving issue by Beatrice, in 1390, João I ruled in peace and pursued the economic development of the country. The exception was the siege and conquer of the city of Ceuta in 1415. After this military success of extreme strategic importance on the control of the navigation in the African coast, João I returned to a non aggressive policy.

Contemporaneous writers describe him as a man of wit, very keen on concentrating the power on himself, but, at the same time, with a benevolent and kind personality. His youth education as Master of a religious order turned him into an unusual learned king in the Middle Ages. His love for knowledge and culture was passed to his sons: Duarte, the future king was a poet and a writer, Pedro, the duke of Coimbra was one of the most learned princes of his time and prince Henry the Navigator, the duke of Viseu, started a school of Navigation and invested heavily on science and development of nautical topics. In 1430, his only surviving daughter, Isabella, married the Philip III, duke of Burgundy and enjoyed an extremely refined court in his lands; she was the mother of Charles the Bold.

João's descendants

• From his wife, Philippa of Lancaster (1359-1415)
  • Branca (1388-1389)
  • Afonso (1390-1400)
  • Duarte, king of Portugal (1391-1438)
  • Pedro, Duke of Coimbra (1392-1449, Battle of Alfarrobeira)
  • Henrique, the Navigator (1394-1460), duke of Viseu
  • Isabel (1397-1471), married to Philip III, duke of Burgundy
  • Branca (1398)
  • João, duke of Aveiro (1400-1442), grandfather of Isabella of Castile
  • Fernando, the Saint Prince (1402-1433), died in captivity in Fez
• From Inês Pires
  • Afonso (1377-1461), first duke of Bragança
  • Beatrice (ca. 1386-1447), married to Thomas Fitzalan, 12th Earl of Arundel

See also: Kings of Portugal family tree